fix: Use QApplication instance as a parent of global actions

[Czaki]

Closes #245

I tested it locally, do not have an idea how to test it on CI.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (06c1bc4) to head (75d8ed9).
⚠️ Report is 16 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #246   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           31        31           
  Lines         1922      1923    +1     
=========================================
+ Hits          1922      1923    +1     

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[tlambert03]

slight preference for this over #247, since A) it still gives the action a parent, which is nice for app-level cleanup, and B) I wonder whether tying the actions to a Menu or Toolbar is too specific?