[release-22.0] Deflake TestVStreamsMetricsErrors. (#18679)

[vitess-bot]

Description

This is a backport of #18679

[vitess-bot]

Hello @arthurschreiber, there are conflicts in this backport.

Please address them in order to merge this Pull Request. You can execute the snippet below to reset your branch and resolve the conflict manually.

Make sure you replace origin by the name of the vitessio/vitess remote

git fetch --all
gh pr checkout 18684 -R vitessio/vitess
git reset --hard origin/release-22.0
git cherry-pick -m 1 e5593a8a123035e13cdf8cb3b6cfcca43745404d

[vitess-bot]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 67.54%. Comparing base (c242fc7) to head (ae66cb3).
⚠️ Report is 129 commits behind head on release-22.0.

Additional details and impacted files

@@               Coverage Diff                @@
##           release-22.0   #18684      +/-   ##
================================================
+ Coverage         67.53%   67.54%   +0.01%     
================================================
  Files              1600     1600              
  Lines            262018   262018              
================================================
+ Hits             176950   176984      +34     
+ Misses            85068    85034      -34     

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[github-actions]

This PR is being marked as stale because it has been open for 30 days with no activity. To rectify, you may do any of the following:

• Push additional commits to the associated branch.
• Remove the stale label.
• Add a comment indicating why it is not stale.

If no action is taken within 7 days, this PR will be closed.

[github-actions]

This PR is being marked as stale because it has been open for 30 days with no activity. To rectify, you may do any of the following:

• Push additional commits to the associated branch.
• Remove the stale label.
• Add a comment indicating why it is not stale.

If no action is taken within 7 days, this PR will be closed.

[github-actions]

This PR is being marked as stale because it has been open for 30 days with no activity. To rectify, you may do any of the following:

• Push additional commits to the associated branch.
• Remove the stale label.
• Add a comment indicating why it is not stale.

If no action is taken within 7 days, this PR will be closed.

[github-actions]

This PR is being marked as stale because it has been open for 30 days with no activity. To rectify, you may do any of the following:

• Push additional commits to the associated branch.
• Remove the stale label.
• Add a comment indicating why it is not stale.

If no action is taken within 7 days, this PR will be closed.

[Copilot]

Pull request overview

Backports the fix from #18679 to deflake TestVStreamsMetricsErrors by removing the test’s dependency on a deterministic ordering between multi-shard VStream event delivery and shard error propagation.

Changes:

• Refactors TestVStreamsMetricsErrors to avoid deadlock by collecting VStream callback results through a channel and waiting for completion deterministically.
• Updates assertions to tolerate the valid race where the non-error shard may or may not emit events before the overall stream is canceled.
• Adjusts vstreams-ended-with-errors metric validation to account for either ordering outcome while still enforcing the error shard’s expected behavior.

[nickvanw]

Upstream has sufficiently diverged that I don't think this is worth it anymore. Closing.