[#27692] Set non-playground Go versions to use Go 1.21.0

[lostluck]

Beam release cut is tomorrow (August 9th, 2023), and Go 1.21.0 was released today, so it's the latest version we can use for the release tomorrow.

Fixes #27692

---

Thank you for your contribution! Follow this checklist to help us incorporate your contribution quickly and easily:

• Mention the appropriate issue in your description (for example: addresses #123), if applicable. This will automatically add a link to the pull request in the issue. If you would like the issue to automatically close on merging the pull request, comment fixes #<ISSUE NUMBER> instead.
• Update CHANGES.md with noteworthy changes.
• If this contribution is large, please file an Apache Individual Contributor License Agreement.

See the Contributor Guide for more tips on how to make review process smoother.

To check the build health, please visit https://github.com/apache/beam/blob/master/.test-infra/BUILD_STATUS.md

GitHub Actions Tests Status (on master branch)

See CI.md for more information about GitHub Actions CI or the workflows README to see a list of phrases to trigger workflows.

[github-actions]

Assigning reviewers. If you would like to opt out of this review, comment assign to next reviewer:

R: @jrmccluskey for label go.
R: @Abacn for label build.

Available commands:

• stop reviewer notifications - opt out of the automated review tooling
• remind me after tests pass - tag the comment author after tests pass
• waiting on author - shift the attention set back to the author (any comment or push by the author will return the attention set to the reviewers)

The PR bot will only process comments in the main thread (not review comments).

[jrmccluskey]

Run Go PreCommit

[jrmccluskey]

This gives us access to slog, right?

[codecov]

Codecov Report

Merging #27900 (c0d8eb8) into master (014a193) will decrease coverage by 0.25%.
Report is 16 commits behind head on master.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #27900      +/-   ##
==========================================
- Coverage   70.83%   70.58%   -0.25%     
==========================================
  Files         861      857       -4     
  Lines      104719   103925     -794     
==========================================
- Hits        74178    73360     -818     
- Misses      28982    29006      +24     
  Partials     1559     1559              

Flag	Coverage Δ
python	79.54% <ø> (-0.28%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

see 20 files with indirect coverage changes

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more

[lostluck]

This gives us access to slog, right?

Technically no. We'd need to update the go.mod version to 1.21 for that, and we are not going to do that before the 2.50 cut tomorrow. We could do it for 2.51 if we like, paired with the change to the standard library version of slog in Prism.

Doing the work of adding a slog handler for beam for 2.51 is a different question entirely.

[jrmccluskey]

I mostly want it for the sections of the boot loaders where we don't have the logging service yet since I'm still living in that world. Noted.

[lostluck]

Sounds good. Also a good reason to move to 1.21, but lets please not make that change the day before the 2.50 cut :).

[jrmccluskey]

LGTM

[lostluck]

Requiring Go 1.21 for beam has a dozen small changes and fixes and documentation bits to update, which we just did for 2.50 to get us to 1.20.

I'd rather avoid skipping release versions, and forcing users that hard to update their Go versions (as unlikely as it is that Beam will be why they do so anyway.)

[lostluck]

The remaining jobs succeeded, github just didn't get the update. Merging.