Avoid ConcurrentModificationException for User class fields

[opensearch-trigger-bot]

Backport 05e56ec from #5084.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 71.52%. Comparing base (dbfecca) to head (8a173a8).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5087   +/-   ##
=======================================
  Coverage   71.52%   71.52%           
=======================================
  Files         336      336           
  Lines       22643    22649    +6     
  Branches     3602     3603    +1     
=======================================
+ Hits        16195    16200    +5     
- Misses       4644     4645    +1     
  Partials     1804     1804           

Files with missing lines	Coverage Δ
...pensearch/security/securityconf/ConfigModelV7.java	73.75% <100.00%> (+0.50%)	⬆️

... and 8 files with indirect coverage changes