[release-21.0] fix SchemaCacheConfig.DefaultExpiration (#17609)

[vitess-bot]

Description

This is a backport of #17609

[vitess-bot]

Review Checklist

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 67.54%. Comparing base (fbee63c) to head (8f67ea0).
Report is 1 commits behind head on release-21.0.

Additional details and impacted files

@@               Coverage Diff                @@
##           release-21.0   #17612      +/-   ##
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+ Coverage         67.52%   67.54%   +0.02%     
================================================
  Files              1570     1570              
  Lines            251512   251512              
================================================
+ Hits             169826   169886      +60     
+ Misses            81686    81626      -60     

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