Use `go-version-file: go.mod` in CI

[timvaillancourt]

Description

This PR uses go-version-file: go.mod in CI that requires a go version == go.mod. This makes the repo a bit easier to maintain in places

The only CI files that still have a specific go-version: set are:

• .github/workflows/upgrade_downgrade_test_backups_e2e.yml
• .github/workflows/upgrade_downgrade_test_backups_manual.yml
• .github/workflows/upgrade_downgrade_test_onlineddl_flow.yml
• .github/workflows/upgrade_downgrade_test_query_serving_queries.yml
• .github/workflows/upgrade_downgrade_test_query_serving_schema.yml
• .github/workflows/upgrade_downgrade_test_reparent_old_vtctl.yml
• .github/workflows/upgrade_downgrade_test_reparent_old_vttablet.yml
• .github/workflows/upgrade_downgrade_test_semi_sync.yml

Are those set by hand? On main these are set to 1.22.7, a previous-release go version. Also I'm unclear if I've broken go-upgrade (I didn't know about this) and could use a hand validating that part 🤔

Example of go-version-file: go.mod finding 1.23.1 (from this PR CI):

Related Issue(s)

https://github.com/vitessio/vitess/issues/16842

Checklist

• [x] "Backport to:" labels have been added if this change should be back-ported to release branches
• [x] If this change is to be back-ported to previous releases, a justification is included in the PR description
• [x] Tests were added or are not required
• [x] Did the new or modified tests pass consistently locally and on CI?
• [x] Documentation was added or is not required

Deployment Notes

[vitess-bot[bot]]

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[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 69.45%. Comparing base (969e018) to head (f8a3984).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #16841 +/- ## ========================================== + Coverage 69.41% 69.45% +0.03% ========================================== Files 1570 1570 Lines 202945 202923 -22 ========================================== + Hits 140880 140940 +60 + Misses 62065 61983 -82 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[systay]

👏 Very nice!

[frouioui]

@frouioui can you also please take a look?

I will take a look at the go-upgrade in the morning

[frouioui]

Are those set by hand?

Yes, these match the golang version used on the previous release branch. Since the goal of these workflows is to downgrade from main to the latest release branch, we use the go version found there.

[timvaillancourt]

Re-requesting review on last tweak from @frouioui 🙇