[3.14] Docs: Upgrade Sphinx to 9.1 (GH-159945) (#161207)

(cherry picked from commit 10bec81)

Co-authored-by: Adam Turner <9087854+AA-Turner@users.noreply.github.com>

Author: StanFromIreland

Doc/requirements.txt

@@ -7,7 +7,7 @@
 # won't suddenly cause build failures. Updating the version is fine as long
 # as no warnings are raised by doing so.
 # Keep this version in sync with ``Doc/conf.py``.
-sphinx<9.0.0
+sphinx~=9.1.1
 
 blurb