Log which tablet copy_state optimization failed on

[mattlord]

Description

This is a minor follow-up to #11451. At the very end of that work I changed the optimizing work so that it's done in a background goroutine for each tablet and the logging of any failures went from the wrangler's logger (vtctl client terminal) to vtctld's warning log. As part of that, however, I should have noted which tablet the work failed on. This PR corrects that.

Related Issue(s)

• Follow-up to: Use unique rows in copy_state to support parallel replication #11451

Checklist

• "Backport me!" label has been added if this change should be backported
• Tests are not required
• Documentation is not required

[vitess-bot]

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