refactor: remove unneeded in Go 1.22 loop var copy

[alexandear]

The PR cleans up unnecessary loop variable copying and enables the copyloopvar linter for detecting this redundant variable copying.

Additional notes

After the project upgraded to Go version 1.22 in #4779, copying variables inside a for loop became unnecessary. See this blog post for a detailed explanation.

The copyloopvar linter is only available from golangci-lint v1.57 onwards, so we also need to update this tool.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.77%. Comparing base (c68d830) to head (8047f89).
Report is 256 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4856      +/-   ##
==========================================
- Coverage   83.77%   83.77%   -0.01%     
==========================================
  Files         135      139       +4     
  Lines       13029    11204    -1825     
==========================================
- Hits        10915     9386    -1529     
+ Misses       1677     1355     -322     
- Partials      437      463      +26     

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[caarlos0]

thank you!