Unpin transformers for pydoc

[riteshghorse]

Since torch is added to autodoc_mock_import, when importing transformers it throws an error when importing from transformers import Pipeline. In one of the steps it checks the torch.__version__. Since this turns out to be None, the transformer import throws an error. This PR adds transformers to autodoc_mock_import as well and unpin transformers version.

Fixes #28104

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[codecov]

Codecov Report

Merging #28436 (d983272) into master (1032533) will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #28436      +/-   ##
==========================================
- Coverage   72.31%   72.30%   -0.01%     
==========================================
  Files         683      683              
  Lines      100633   100633              
==========================================
- Hits        72768    72765       -3     
- Misses      26289    26292       +3     
  Partials     1576     1576              

Flag	Coverage Δ
python	82.82% <ø> (-0.01%)	⬇️

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[riteshghorse]

R: @damccorm

[damccorm]

Nice!