fix: data race for for Barrier::Wait()

[BorysTheDev]

cond_.notify_all() accesses unprotected wait_queue, therefore it must be under lock.
The problem was found in https://github.com/dragonflydb/dragonfly/actions/runs/11343555702/job/31546353995?pr=3924#step:12:818

[codecov-commenter]

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.44%. Comparing base (d30de86) to head (17c4307).
Report is 100 commits behind head on master.

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #324      +/-   ##
==========================================
+ Coverage   77.60%   78.44%   +0.83%     
==========================================
  Files         103      108       +5     
  Lines        7824     8558     +734     
==========================================
+ Hits         6072     6713     +641     
- Misses       1752     1845      +93     

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