doc/sphinx: Bump Jinja2 to 3.1.4

While we unlikely to have an issue with CVE-2024-22195, it is simple
enough to bump our version of Jinja2 to receive the fix, do so.

Reported-by: GitHub dependabot
Tested-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Tom Rini <trini@konsulko.com>