[FIX] Fix test_overlay

[ales-erjavec]

Issue

Tests fail with a segmentation fault when running under pytest>=8.2

Changes

• Dispatch to super class setUp/tearDown in TestOverlay
• Replace use of Mock in signal connection with QSignalSpy

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 76.67%. Comparing base (6967b60) to head (4a878c7).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #299      +/-   ##
==========================================
+ Coverage   76.63%   76.67%   +0.04%     
==========================================
  Files          99       99              
  Lines       21101    21101              
==========================================
+ Hits        16170    16179       +9     
+ Misses       4931     4922       -9     

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