Revert "doc: ci: Zephyr now requires Python 3.12 or higher"

This reverts commit 043bb584.

Note that  scripts/requirements-actions.txt might not be 100% the same
as what was pinned prior to the revert due to it being difficult to
restore previous versions while also accounting for the new dependencies
that were added in the meantime.

Signed-off-by: Benjamin Cabé <benjamin@zephyrproject.org>