[release-21.0] Backport: Fix GetSchema RPC to prevent returning view definitions when EnableViews is disabled

[harshit-gangal]

This PR is backport of #18513

[vitess-bot]

Review Checklist

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[codecov]

Codecov Report

❌ Patch coverage is 0% with 12 lines in your changes missing coverage. Please review.
✅ Project coverage is 67.54%. Comparing base (e3ee878) to head (806db4d).
⚠️ Report is 1 commits behind head on release-21.0.

Files with missing lines	Patch %	Lines
go/vt/vttablet/tabletserver/query_executor.go	0.00%	12 Missing ⚠️

Additional details and impacted files

@@               Coverage Diff                @@
##           release-21.0   #18734      +/-   ##
================================================
- Coverage         67.55%   67.54%   -0.02%     
================================================
  Files              1572     1572              
  Lines            252526   252536      +10     
================================================
- Hits             170596   170571      -25     
- Misses            81930    81965      +35     

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