fix: Fixed TransformerDecoder for PyTorch 1.10

[fg-mindee]

This PR simply makes transformer-based models of DocTR compatible with the latest PyTorch release.

Any feedback is welcome!

[charlesmindee]

Thanks for that, it is a good thing they added the option!

[codecov]

Codecov Report

Merging #539 (a94d4c4) into main (3c7303c) will increase coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #539      +/-   ##
==========================================
+ Coverage   95.36%   95.38%   +0.02%     
==========================================
  Files         109      109              
  Lines        4184     4182       -2     
==========================================
- Hits         3990     3989       -1     
+ Misses        194      193       -1     

Flag	Coverage Δ
unittests	95.38% <ø> (+0.02%)	⬆️

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Impacted Files	Coverage Δ
doctr/models/recognition/transformer/pytorch.py	100.00% <ø> (ø)
...dels/detection/differentiable_binarization/base.py	91.82% <0.00%> (+0.62%)	⬆️

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