CI: Improve reliability of codecov workflow with larger runner

[mattlord]

Description

The codecov workflow has been VERY flaky lately. Typically taking 3+ attempts before it succeeds. This workflow runs every unit test with code coverage enabled — so it's heavier than our other unit test workflows which have split off the evalengine tests into a separate workflow — and the failures I kept seeing made no sense, unless we were resource starved. So to test that theory I used a larger runner (up until 9 months ago, we were using a larger one). You can see the results here from 10 runs: https://github.com/vitessio/vitess/actions/runs/19942952837?pr=18992

We went from having to run it 2-5 times to get it to pass once, so let's say it was passing ~ 30% of the time. Whereas on this branch it passed 7 out of 10 times, so 70%. That is pretty good, considering that we DO have a number of flaky individual unit tests.

Note

Backporting to v22 so that we have an improved CI for all supported release branches.

Related Issue(s)

Checklist

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

AI Disclosure

[vitess-bot]

Review Checklist

Hello reviewers! 👋 Please follow this checklist when reviewing this Pull Request.

General

• Ensure that the Pull Request has a descriptive title.
• Ensure there is a link to an issue (except for internal cleanup and flaky test fixes), new features should have an RFC that documents use cases and test cases.

Tests

• Bug fixes should have at least one unit or end-to-end test, enhancement and new features should have a sufficient number of tests.

Documentation

• Apply the release notes (needs details) label if users need to know about this change.
• New features should be documented.
• There should be some code comments as to why things are implemented the way they are.
• There should be a comment at the top of each new or modified test to explain what the test does.

New flags

• Is this flag really necessary?
• Flag names must be clear and intuitive, use dashes (-), and have a clear help text.

If a workflow is added or modified:

• Each item in Jobs should be named in order to mark it as required.
• If the workflow needs to be marked as required, the maintainer team must be notified.

Backward compatibility

• Protobuf changes should be wire-compatible.
• Changes to _vt tables and RPCs need to be backward compatible.
• RPC changes should be compatible with vitess-operator
• If a flag is removed, then it should also be removed from vitess-operator and arewefastyet, if used there.
• vtctl command output order should be stable and awk-able.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 69.85%. Comparing base (d411dd0) to head (fe82939).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #18992      +/-   ##
==========================================
+ Coverage   69.82%   69.85%   +0.03%     
==========================================
  Files        1610     1610              
  Lines      215303   215303              
==========================================
+ Hits       150328   150398      +70     
+ Misses      64975    64905      -70     

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[timvaillancourt]

— and the failures I kept seeing made no sense, unless we were resource starved.

@mattlord nice catch! I've been looking into this as well and was a bit lost 🚀