Limit sphinx-autodoc-typehints upper bound

[ascillitoe]

Limit sphinx-autodoc-typehints to <1.19.3 due to tox-dev/sphinx-autodoc-typehints#259 and tox-dev/sphinx-autodoc-typehints#260.

alibi-detect equivalent: SeldonIO/alibi-detect#633

[ascillitoe]

@jklaise the docs CI is now passing 👍🏻

[codecov]

Codecov Report

Merging #790 (cab928b) into master (ee7c166) will decrease coverage by 0.14%.
The diff coverage is n/a.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #790      +/-   ##
==========================================
- Coverage   75.72%   75.57%   -0.15%     
==========================================
  Files          72       72              
  Lines        8223     8190      -33     
==========================================
- Hits         6227     6190      -37     
- Misses       1996     2000       +4     

Flag	Coverage Δ
macos-latest-3.10.6	?
ubuntu-latest-3.10.6	?
ubuntu-latest-3.7	?
ubuntu-latest-3.8	75.48% <ø> (-0.10%)	⬇️
ubuntu-latest-3.9	75.57% <ø> (ø)
windows-latest-3.9	?

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
alibi/utils/discretizer.py	92.50% <0.00%> (-5.00%)	⬇️
alibi/explainers/ale.py	65.21% <0.00%> (-0.44%)	⬇️
alibi/utils/approximation_methods.py	81.81% <0.00%> (-0.41%)	⬇️
alibi/explainers/partial_dependence.py	47.73% <0.00%> (-0.22%)	⬇️
alibi/explainers/anchors/anchor_text.py	94.30% <0.00%> (-0.14%)	⬇️
alibi/explainers/cfrl_base.py	87.79% <0.00%> (-0.09%)	⬇️
alibi/explainers/shap_wrappers.py	92.27% <0.00%> (-0.02%)	⬇️
alibi/api/defaults.py	100.00% <0.00%> (ø)