test: Fixed ColorInversion unittest

[fg-mindee]

This PR fixes the edge case on the unittest of ColorInversion

[charlesmindee]

Thanks!

[codecov]

Codecov Report

Merging #298 (5007c51) into main (f6b0ff9) will decrease coverage by 0.04%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #298      +/-   ##
==========================================
- Coverage   96.09%   96.04%   -0.05%     
==========================================
  Files          48       48              
  Lines        2124     2124              
==========================================
- Hits         2041     2040       -1     
- Misses         83       84       +1     

Flag	Coverage Δ
unittests	96.04% <ø> (-0.05%)	⬇️

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Impacted Files	Coverage Δ
...tr/models/detection/differentiable_binarization.py	93.25% <0.00%> (-0.40%)	⬇️

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