Cap the Markdown dependency on Python to 3.3.x.
Review Request #12478 — Created July 19, 2022 and submitted
Python-Markdown 3.4 released this week, and broke compatibility with
our version of
pymdownx, and removed support for Python 3.6.
To avoid any unexpected issues, we're capping the version to 3.3.x. This
will apply to Review Board 4 and 5 beta 1.
Installed Python 3.6 and 3.10 builds and saw that Markdown 3.3.x was used.
Unit tests pass.