fix SchemaCacheConfig.DefaultExpiration

[mcrauwel]

Description

fixing the cache duration for the SchemaCacheConfig items

Backport reason: bug affecting users requiring at least v20.

Related Issue(s)

fixes #17608

Checklist

• "Backport to:" labels have been added if this change should be back-ported to release branches
• If this change is to be back-ported to previous releases, a justification is included in the PR description
• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on CI?
• Documentation was added or is not required

Deployment Notes

[vitess-bot]

Review Checklist

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[notfelineit]

Thanks Matthias! :)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 67.66%. Comparing base (d1aa2f4) to head (229db8f).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #17609      +/-   ##
==========================================
- Coverage   67.68%   67.66%   -0.03%     
==========================================
  Files        1586     1586              
  Lines      255170   255403     +233     
==========================================
+ Hits       172722   172828     +106     
- Misses      82448    82575     +127     

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