Dev/no lock

[kristjanvalur]

Pull Request check-list

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• Does $ tox pass with this change (including linting)?
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Description of change

An asyncio.Lock present around the redis.asyncio.Connection._parser.read_response() is removed. This is not required, since only a single task should be sending/receiving on a single Connection at the same time.
There is no lock around the send() code and
Without a lock around the entire execute_command() (send, and receive) there has been no guarantee that a response is returned which matches the sent command, if more than one task are sending.

A single unittest for concurrent execution was skipped to not run in single-connection mode. This unittest would have also sporadically failed before this PR if the concurrent commands were different. As it happened, all 10 were the exact same ping command and so mismatching requests/responses were never detected.

[codecov-commenter]

Codecov Report

Merging #2308 (b5ebada) into master (b5ebada) will not change coverage.
The diff coverage is n/a.

❗ Current head b5ebada differs from pull request most recent head 8d86e87. Consider uploading reports for the commit 8d86e87 to get more accurate results

@@           Coverage Diff           @@
##           master    #2308   +/-   ##
=======================================
  Coverage   92.21%   92.21%           
=======================================
  Files         111      111           
  Lines       28781    28781           
=======================================
  Hits        26539    26539           
  Misses       2242     2242           

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[kristjanvalur]

As usual, sporadic CI failures with docker.

[kristjanvalur]

This PR, if accepted, will impact #2295 and make it simpler.

[kristjanvalur]

🍾