Fix override of channel_name in Suite2pSegmentationExtractor

[weiglszonja]

Fix an oversight from my side in #242 which overrides channel_name and leads to incorrect reading of the mean image.

[CodyCBakerPhD]

@weiglszonja Can you think of any way to add a test for this?

[codecov]

Codecov Report

Merging #263 (3ca299f) into main (abe24d7) will decrease coverage by 0.01%.
Report is 1 commits behind head on main.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #263      +/-   ##
==========================================
- Coverage   79.01%   79.00%   -0.01%     
==========================================
  Files          39       39              
  Lines        3031     3030       -1     
==========================================
- Hits         2395     2394       -1     
  Misses        636      636              

Flag	Coverage Δ
unittests	79.00% <100.00%> (-0.01%)	⬇️

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Files	Coverage Δ
...extractors/suite2p/suite2psegmentationextractor.py	89.54% <100.00%> (-0.07%)	⬇️