CHANGELOG: update CHANGELOG-3.5.md

[fuweid]

• add item: support custom content check offline in v2store

REF: #19113

Please read https://github.com/etcd-io/etcd/blob/main/CONTRIBUTING.md#contribution-flow.

[fuweid]

ping @ahrtr

[k8s-ci-robot]

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.79%. Comparing base (b4450d5) to head (df209ba).
Report is 58 commits behind head on main.

Additional details and impacted files

see 37 files with indirect coverage changes

@@            Coverage Diff             @@
##             main   #19151      +/-   ##
==========================================
- Coverage   68.82%   68.79%   -0.04%     
==========================================
  Files         420      420              
  Lines       35627    35649      +22     
==========================================
+ Hits        24520    24523       +3     
- Misses       9679     9701      +22     
+ Partials     1428     1425       -3     

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