Add test for duplicate columns

[mumichae]

Close #311

[codecov]

Codecov Report

Merging #311 (3cde909) into main (9628f5b) will increase coverage by 0.24%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #311      +/-   ##
==========================================
+ Coverage   60.16%   60.40%   +0.24%     
==========================================
  Files          40       40              
  Lines        2149     2157       +8     
==========================================
+ Hits         1293     1303      +10     
+ Misses        856      854       -2     

Flag	Coverage Δ
unittest	60.40% <100.00%> (+0.24%)	⬆️

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Impacted Files	Coverage Δ
tests/integration/test_scanorama.py	100.00% <ø> (ø)
tests/preprocessing/test_preprocessing.py	100.00% <100.00%> (ø)
scib/utils.py	72.72% <0.00%> (+4.54%)	⬆️