Fix ReloadSchema incorrectly using DisableBinlogs value in grpctmclient

[mhamza15]

Description

Fixes a small bug where ReloadSchema was incorrectly set to req.DisableBinlogs instead of req.ReloadSchema in ExecuteFetchAsDba and ExecuteMultiFetchAsDba.

Some backup test cases broke as a result of this fix, since they silently relied on the fact ExecuteFetchAsDba wasn't properly reloading the schema cache. Fixed by resetting test state in between runs.

Related Issue(s)

Checklist

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[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 69.89%. Comparing base (ffa1e9b) to head (8e237fb).
⚠️ Report is 12 commits behind head on main.

Files with missing lines	Patch %	Lines
go/vt/vttablet/grpctmclient/client.go	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #19085      +/-   ##
==========================================
+ Coverage   69.88%   69.89%   +0.01%     
==========================================
  Files        1612     1613       +1     
  Lines      215822   216023     +201     
==========================================
+ Hits       150828   150996     +168     
- Misses      64994    65027      +33     

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