VDiff: Handle read only error

[twthorn]

Description

This error happens during VDiff and reparents, so we should catch it not fail to client/command status.

Related Issue(s)

Slack context

Checklist

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• Documentation was added or is not required

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[promptless]

📝 Documentation updates detected!

New suggestion: Add v24.0.0 changelog entry for VDiff reparent error handling improvement

[codecov]

Codecov Report

❌ Patch coverage is 66.66667% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 69.82%. Comparing base (d411dd0) to head (5f7d3e8).
⚠️ Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
go/vt/vttablet/tabletmanager/vdiff/controller.go	33.33%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #18999   +/-   ##
=======================================
  Coverage   69.82%   69.82%           
=======================================
  Files        1610     1610           
  Lines      215303   215309    +6     
=======================================
+ Hits       150328   150341   +13     
+ Misses      64975    64968    -7     

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[timvaillancourt]

@twthorn / @mattlord: I wonder if we should explain that this may be caused by a reparent, or is that too much information?

[timvaillancourt]

@twthorn thanks, this LGTM 👍

[mattlord]

@twthorn can you please open an issue describing the problem you are trying to solve here?

From there, why do you think this new behavior is correct. And why do you think it's better?

We can't make a change like this w/o endtoend test coverage.

[mattlord]

We cannot accept changes w/o clearly identifying the problem/issue, why the new behavior is correct and an improvement, and w/o some endtoend test coverage.