CI Bug: Rename shard name back to match existing workflow file for vreplication_migrate_vdiff2_convert_tz

[rohit-nayak-ps]

Description

This PR makes two changes:

• The shard name vreplication_migrate_vdiff2_convert_tz was changed in PR VReplication: Fix vtctldclient SwitchReads related bugs and move the TestBasicV2Workflows e2e test to vtctldclient #15579 but the workflow file was not renamed. Hence the related tests are no longer running in CI. This PR changes it back, so we can continue to use the same workflow name to avoid having to update the list of Required actions ...

• Cluster 22 was no longer necessary after Delete all legacy sharding related code #10278. Deleted that shard and removed the workflow from the Required set in the GitHub Repo Settings.

Related Issue(s)

#15579
#10278

Checklist

• "Backport to:" labels have been added if this change should be back-ported to release branches
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• Documentation was added or is not required

Deployment Notes

[vitess-bot]

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