Pin Jinja2 for doc builds (#8773) (#8910)

The latest jinja2 breaks Sphinx 3.x builds. For now, pinning jinja2 to
an earlier release for doc builds.

(cherry picked from commit d9eeca39b7910e0b35d213a3c9be58e1edf01a53)

Co-authored-by: Brian Neradt <brian.neradt@gmail.com>
1 file changed