fix: update Qt.LeftButton usage for PyQt6

[RaghavaAlajangi]

This PR aims to fix issue #88

[RaghavaAlajangi]

Hi @paulmueller
Please look at this change.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 71.62%. Comparing base (a301074) to head (b6d0024).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
dcoraid/gui/dbview/drag_table_widget.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #90      +/-   ##
==========================================
+ Coverage   71.55%   71.62%   +0.06%     
==========================================
  Files          52       52              
  Lines        4571     4571              
==========================================
+ Hits         3271     3274       +3     
+ Misses       1300     1297       -3     

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