Make connection initialize flag works as expected

[YorigamiShion]

I think flag atomicBoolean here is expected to make sure only one thread executes sync.getConncetion().whenComplete to remove the Sync from map when init is fail. However, the original implmentation will allow all threads execute whenComplete if the connection is not initialized.
Furthermore, call connections.get then connections.computeIfAbsent is unnecessary.

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.69%. Comparing base (43843bf) to head (004b471).
Report is 251 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #2835      +/-   ##
============================================
- Coverage     78.71%   77.69%   -1.03%     
- Complexity     6786     7236     +450     
============================================
  Files           508      539      +31     
  Lines         22765    24492    +1727     
  Branches       2446     2606     +160     
============================================
+ Hits          17919    19028    +1109     
- Misses         3717     4266     +549     
- Partials       1129     1198      +69     

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[mp911de]

Care to elaborate what kind of issue you're addressing before we jump right into the code?