[ci] Fix for recent breakage of CI due to a jinja2 update
Summary
This pins the jinja2 version to 3.0.0 which doesn't have the API breakage and broke mkdocs.
Background: We were getting CI failures after a package we depend on for the "pages" CI step (mkdocs) failed to operate correctly due to a dependency it has (jinja2) changing its API.
See: https://github.com/mkdocs/mkdocs/issues/2799
Test Plan
Ensure CI succeeds now after this change by observing the pipeline not fail.