build: use pyqt6 for dev extra

[tlambert03]

No description provided.

[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (15fe70c) 89.76% compared to head (f046e0c) 89.77%.
Report is 6 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #569   +/-   ##
=======================================
  Coverage   89.76%   89.77%           
=======================================
  Files          37       37           
  Lines        4434     4438    +4     
=======================================
+ Hits         3980     3984    +4     
  Misses        454      454           

see 5 files with indirect coverage changes

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