Pin sphinx != 6.1.2

Sphinx 6.1.2 introduces new behavior which causes python source files to
be copied into the images folder errantly.

For a more full write up refer to sphinx-doc/sphinx#11117

requirements/doc/doc-requirements.txt

@@ -7,7 +7,7 @@
 # Install the documentation requirements with:
 #     pip install -r requirements/doc/doc-requirements.txt
 #
-sphinx>=3.0.0
+sphinx>=3.0.0,!=6.1.2
 colorspacious
 ipython
 ipywidgets