[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 :white_check_mark:

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

Additional details and impacted files

```diff @@ 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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