Update build doc config, still running into rtd build issues which don't happen locally :-/

Author: vincefn

doc/environment.yml

@@ -7,7 +7,7 @@ dependencies:
   - pydata-sphinx-theme
   - docutils=0.20.1    # https://github.com/vidartf/nbsphinx-link/issues/22
   - m2r2
-  - nbsphinx
+  - nbsphinx=6.4.3     # https://github.com/jupyter/nbconvert/issues/1742
   - nbsphinx-link
   - numpy
   - lxml-html-clean