Fix mpl-sphinx-theme pinning

Co-authored-by: Elliott Sales de Andrade <[email protected]>

Author: dstansby

requirements/requirements.in

@@ -9,7 +9,7 @@ pip-tools
 pre-commit
 scipy
 # Docs
-mpl-sphinx-theme~=3.8
+mpl-sphinx-theme~=3.8.0
 pydata-sphinx-theme==0.13.3
 sphinx
 sphinx-design