fix: allow older qtpy

[tlambert03]

catch from qtpy import QT6

[codecov]

Codecov Report

Merging #37 (32afd7a) into main (ba97ec6) will decrease coverage by 0.05%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##             main      #37      +/-   ##
==========================================
- Coverage   97.70%   97.64%   -0.06%     
==========================================
  Files          31       31              
  Lines        1611     1614       +3     
==========================================
+ Hits         1574     1576       +2     
- Misses         37       38       +1     

Impacted Files	Coverage Δ
src/app_model/backends/qt/_qmenubar.py	0.00% <0.00%> (ø)
src/app_model/backends/qt/_qkeymap.py	100.00% <100.00%> (ø)
src/app_model/backends/qt/_qmenu.py	94.89% <100.00%> (+0.05%)	⬆️

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