fix: WeasyPrint version compatibility with Python 3.7

[charlesmindee]

This PR forces the weasyprint version to 52.5 because we have a bug showing up with the 53.0 version with python 3.7
Any feedback is welcome!

Closes #401

[fg-mindee]

Thanks! I suggested an extra flexibility of weasyprint version constraints rather than pinning it

[codecov]

Codecov Report

Merging #404 (4945947) into main (d15725a) will increase coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #404      +/-   ##
==========================================
+ Coverage   95.88%   95.91%   +0.02%     
==========================================
  Files          91       91              
  Lines        3795     3795              
==========================================
+ Hits         3639     3640       +1     
+ Misses        156      155       -1     

Flag	Coverage Δ
unittests	95.91% <ø> (+0.02%)	⬆️

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Impacted Files	Coverage Δ
doctr/models/core.py	94.95% <0.00%> (+0.84%)	⬆️

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[fg-mindee]

Thanks!