CI: add flock test

[zhoucheng361]

No description provided.

[github-actions]

Mutate Test Report

Usage: https://github.com/juicedata/juicefs/blob/main/.github/scripts/mutate/how_to_use_mutate_test.md

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (9a40759) 55.57% compared to head (79b4b52) 55.60%.
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4203      +/-   ##
==========================================
+ Coverage   55.57%   55.60%   +0.02%     
==========================================
  Files         154      154              
  Lines       39492    39492              
==========================================
+ Hits        21949    21959      +10     
+ Misses      15085    15078       -7     
+ Partials     2458     2455       -3     

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