test: fixes for pymmcore v11.5

[tlambert03]

the new version of pymmcore changes a few things that break tests. This fixes it. see also micro-manager/pymmcore#131

[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 12 lines in your changes missing coverage. Please review.

Project coverage is 91.09%. Comparing base (e7a6153) to head (f050737).
Report is 7 commits behind head on main.

Files with missing lines	Patch %	Lines
src/pymmcore_plus/model/_config_file.py	58.33%	5 Missing ⚠️
src/pymmcore_plus/metadata/functions.py	50.00%	3 Missing ⚠️
src/pymmcore_plus/model/_pixel_size_config.py	66.66%	3 Missing ⚠️
src/pymmcore_plus/core/_mmcore_plus.py	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #451      +/-   ##
==========================================
- Coverage   91.51%   91.09%   -0.42%     
==========================================
  Files          62       62              
  Lines        5277     5322      +45     
==========================================
+ Hits         4829     4848      +19     
- Misses        448      474      +26     

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[codspeed-hq]

CodSpeed Performance Report

Merging #451 will not alter performance

_{Comparing tlambert03:fix-tests (f050737) with main (0b7a74a)}

Summary

✅ 7 untouched benchmarks

[tlambert03]

the only failing tests now needs to be fixed on the pymmcore-widgets side: pymmcore-plus/pymmcore-widgets#414