docs: Fixed documentation build

[fg-mindee]

This PR introduces the following modifications:

• cleans up the remaining files after multi-version build
• fixed a silent fail of git checkout because of untracked files (which are now removed once the specific doc version is built)

Any feedback is welcome!

[charlesmindee]

Thanks

[codecov]

Codecov Report

Merging #644 (5c1bb28) into main (0aa4bb1) will decrease coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #644      +/-   ##
==========================================
- Coverage   96.09%   96.07%   -0.03%     
==========================================
  Files         112      112              
  Lines        4357     4357              
==========================================
- Hits         4187     4186       -1     
- Misses        170      171       +1     

Flag	Coverage Δ
unittests	96.07% <ø> (-0.03%)	⬇️

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Impacted Files	Coverage Δ
...dels/detection/differentiable_binarization/base.py	91.19% <0.00%> (-0.63%)	⬇️

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