Fix db lock tests

[callebtc]

Skip some SQLite db locking tests on github only for regtest + sqlite

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 1 line in your changes missing coverage. Please review.

Project coverage is 66.94%. Comparing base (48b0368) to head (c801f3b).
Report is 10 commits behind head on main.

Files with missing lines	Patch %	Lines
cashu/core/db.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #665      +/-   ##
==========================================
+ Coverage   66.56%   66.94%   +0.37%     
==========================================
  Files          81       81              
  Lines        8366     8394      +28     
==========================================
+ Hits         5569     5619      +50     
+ Misses       2797     2775      -22     

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