[8.0.x] Disallow Sphinx 6 and 7 (#12001)

Co-authored-by: Bruno Oliveira <[email protected]>

Author: github-actions[bot]

Diff for: doc/en/requirements.txt

@@ -2,7 +2,8 @@ pallets-sphinx-themes
 pluggy>=1.2.0
 pygments-pytest>=2.3.0
 sphinx-removed-in>=0.2.0
-sphinx>=5,<8
+# In Sphinx 6 and 7, the search bar disappears; restrict this for now until we find a solution.
+sphinx>=5,<6
 sphinxcontrib-trio
 sphinxcontrib-svg2pdfconverter
 # Pin packaging because it no longer handles 'latest' version, which