try pinning jinja2 again

Author: cole

docs/requirements.txt

@@ -1,3 +1,4 @@
 # Required by Read the Docs.
 sphinx>=4,<5
 sphinx_autodoc_typehints>=1.7,<2
+jinja2>=3.0,<3.1  # fix sphinx failing, see: https://github.com/sphinx-doc/sphinx/issues/10291

tox.ini

@@ -48,11 +48,12 @@ commands =
     coverage erase
 
 [testenv:docs]
-basepython = python3.8
+basepython = python3.9
 deps =
     {[testenv]deps}
     sphinx>=4,<5
     sphinx_autodoc_typehints>=1.7,<2
+    jinja2>=3.0,<3.1  # fix sphinx failing, see: https://github.com/sphinx-doc/sphinx/issues/10291
 changedir = docs
 commands =
     sphinx-build {posargs:-nWT} -b doctest -d {envtmpdir}/doctrees . {envtmpdir}/html