build(deps): Bump redis from 3.2.1 to 3.3.5 in /backend

[dependabot-preview]

Bumps redis from 3.2.1 to 3.3.5.

Changelog

Sourced from redis's changelog.

• 3.3.5
  • Fix an issue where socket.timeout errors could be handled by the wrong
    exception handler in Python 2.7.
• 3.3.4
  • More specifically identify nonblocking read errors for both SSL and
    non-SSL connections. 3.3.1, 3.3.2 and 3.3.3 on Python 2.7 could
    potentially mask a ConnectionError. #1197
• 3.3.3
  • The SSL module in Python < 2.7.9 handles non-blocking sockets
    differently than 2.7.9+. This patch accommodates older versions. #1197
• 3.3.2
  • Further fixed a regression introduced in 3.3.0 involving SSL and
    non-blocking sockets. #1197
• 3.3.1
  • Fixed a regression introduced in 3.3.0 involving SSL and non-blocking
    sockets. #1197
• 3.3.0
  • Resolve a race condition with the PubSubWorkerThread. #1150
  • Cleanup socket read error messages. Thanks Vic Yu. #1159
  • Cleanup the Connection's selector correctly. Thanks Bruce Merry. #1153
  • Added a Monitor object to make working with MONITOR output easy.
    Thanks Roey Prat #1033
  • Internal cleanup: Removed the legacy Token class which was necessary
    with older version of Python that are no longer supported. #1066
  • Response callbacks are now case insensitive. This allows users that
    call Redis.execute_command() directly to pass lower-case command
    names and still get reasonable responses. #1168
  • Added support for hiredis-py 1.0.0 encoding error support. This should
    make the PythonParser and the HiredisParser behave identically
    when encountering encoding errors. Thanks Brian Candler. #1161/#1162
  • All authentication errors now properly raise AuthenticationError.
    AuthenticationError is now a subclass of ConnectionError, which will
    cause the connection to be disconnected and cleaned up appropriately.
    #923
  • Add READONLY and READWRITE commands. Thanks @​theodesp. #1114
  • Remove selectors in favor of nonblocking sockets. Selectors had
    issues in some environments including eventlet and gevent. This should
    resolve those issues with no other side effects.
  • Fixed an issue with XCLAIM and previously claimed but not removed
    messages. Thanks @​thomdask. #1192/#1191
  • Allow for single connection client instances. These instances
    are not thread safe but offer other benefits including a subtle
    performance increase.
  • Added extensive health checks that keep the connections lively.
    Passing the "health_check_interval=N" option to the Redis client class
    or to a ConnectionPool ensures that a round trip PING/PONG is successful
    before any command if the underlying connection has been idle for more
    than N seconds. ConnectionErrors and TimeoutErrors are automatically
    retried once for health checks.
  • Changed the PubSubWorkerThread to use a threading.Event object rather

... (truncated)

Commits

• a5ba696 version 3.3.5, handle socket.timeout errors correctly in Python 2.7
• 3afa016 version 3.3.4, more specifically identify nonblocking read errors
• 885ce77 version 3.3.4, more specifically identify nonblocking read errors
• 6b6e394 fixed some misspellings in the changes file
• f966b64 Version 3.3.3. Accomodate Python 2.7.x versions < 2.7.9.
• c1b9941 Make pubsub tests more resilient on laggy connections
• a99f389 use a multi-connection client for multiprocess tests
• f307878 Version 3.3.2, SSL Blocking Exceptions don't use errno.EWOULDBLOCK
• e897c17 version 3.3.1, fixed a regression involving SSL and non-blocking sockets
• 0de7c82 clearer language in docs
• Additional commits viewable in compare view

Dependabot will resolve any conflicts with this PR as long as you don't alter it yourself. You can also trigger a rebase manually by commenting @dependabot rebase.

---

Dependabot commands and options

You can trigger Dependabot actions by commenting on this PR:

• @dependabot rebase will rebase this PR
• @dependabot recreate will recreate this PR, overwriting any edits that have been made to it
• @dependabot merge will merge this PR after your CI passes on it
• @dependabot squash and merge will squash and merge this PR after your CI passes on it
• @dependabot cancel merge will cancel a previously requested merge and block automerging
• @dependabot reopen will reopen this PR if it is closed
• @dependabot ignore this [patch|minor|major] version will close this PR and stop Dependabot creating any more for this minor/major version (unless you reopen the PR or upgrade to it). To ignore the version in this PR you can just close it
• @dependabot ignore this dependency will close this PR and stop Dependabot creating any more for this dependency (unless you reopen the PR or upgrade to it yourself)
• @dependabot use these labels will set the current labels as the default for future PRs for this repo and language
• @dependabot use these reviewers will set the current reviewers as the default for future PRs for this repo and language
• @dependabot use these assignees will set the current assignees as the default for future PRs for this repo and language
• @dependabot use this milestone will set the current milestone as the default for future PRs for this repo and language
• @dependabot badge me will comment on this PR with code to add a "Dependabot enabled" badge to your readme

Additionally, you can set the following in your Dependabot dashboard:

• Update frequency (including time of day and day of week)
• Automerge options (never/patch/minor, and dev/runtime dependencies)
• Pull request limits (per update run and/or open at any time)
• Out-of-range updates (receive only lockfile updates, if desired)
• Security updates (receive only security updates, if desired)

Finally, you can contact us by mentioning @dependabot.

[dependabot-preview]

A newer version of redis exists, but since this PR has been edited by someone other than Dependabot I haven't updated it. You'll get a PR for the updated version as normal once this PR is merged.

[dependabot-preview]

OK, I won't notify you again about this release, but will get in touch when a new version is available. If you'd rather skip all updates until the next major or minor version, let me know by commenting @dependabot ignore this major version or @dependabot ignore this minor version.

If you change your mind, just re-open this PR and I'll resolve any conflicts on it.