chore: release 2.21.0

[release-please]

🤖 I have created a release *beep* *boop*

2.21.0 (2021-07-13)

Features

• add always_use_jwt_access (#714) (92fbd4a)
• add max_results parameter to some of the QueryJob methods (#698) (2a9618f)
• add support for decimal target types (#735) (7d2d3e9)
• add support for table snapshots (#740) (ba86b2a)
• enable unsetting policy tags on schema fields (#703) (18bb443)
• make it easier to disable best-effort deduplication with streaming inserts (#734) (1246da8)
• Support passing struct data to the DB API (#718) (38b3ef9)

Bug Fixes

• inserting non-finite floats with insert_rows() (#728) (d047419)
• use pandas function to check for NaN (#750) (67bc5fb)

Documentation

• add docs for all enums in module (#745) (145944f)
• omit mention of Python 2.7 in CONTRIBUTING.rst (#706) (27d6839)

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This PR was generated with Release Please. See documentation.

[tseaver]

@tswast, @busunkim96 Can we figure out how to get the bot to give up on this one?

[tswast]

Looks like the tag wasn't created quite right after #753

[tswast]

I manually created https://github.com/googleapis/python-bigquery/releases/tag/v2.21.0

Hopefully that fixes it.

[plamut]

For more context, I primarily created a release PR manually to assure the release notes were sound. Apart from punctuation, which is nice but minor, the main reason was to exclude a CHANGELOG entry that was later reverted, but the bot re-introduced it when re-generating the release notes as PRs got merged.

In other words, it would be good to have more control over the bot through release PR edits, if that's possible.

[tswast]

Word is that it's the release PR branch that is used to determine if to open a PR.

@plamut Were you not able to commit changes to the release branch? Maybe we need to figure out some permissions.

[tswast]

googleapis/release-please#967 has been filed to improve the CHANGELOG edit flow

Merging #760 before we make any releasable commits should fix it.

[plamut]

@tswast The bot was overriding a reverted change in the changelog, it kept adding it back with every new PR. And I wanted to polish a few other things, too, thus forged the original PR branch and submitted it.

I'll report the observed quirks to release-please tomorrow.