fix: fix valueChanged signals on PropertyWidget

[tlambert03]

wasn't getting emitted properly

[codecov]

Codecov Report

Attention: Patch coverage is 81.81818% with 2 lines in your changes missing coverage. Please review.

Project coverage is 90.60%. Comparing base (013635e) to head (091103e).
Report is 17 commits behind head on main.

Files with missing lines	Patch %	Lines
src/pymmcore_widgets/_property_widget.py	81.81%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #352   +/-   ##
=======================================
  Coverage   90.59%   90.60%           
=======================================
  Files          74       74           
  Lines        8393     8396    +3     
=======================================
+ Hits         7604     7607    +3     
  Misses        789      789           

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