Infra: bump Sphinx to >=9.1, limit docutils to <0.22

Author: Secrus

requirements.txt

@@ -1,10 +1,8 @@
 # Requirements for building PEPs with Sphinx
 # Sphinx requires >= 2.17. JSON5 support added in 2.19
 Pygments >= 2.19
-# Sphinx 6.1.0 broke copying images in parallel builds; fixed in 6.1.2
-# See https://github.com/sphinx-doc/sphinx/pull/11100
-Sphinx >= 5.1.1, != 6.1.0, != 6.1.1, < 8.1.0
-docutils >= 0.19.0
+Sphinx >= 9.1.0 
+docutils >= 0.19.0, < 0.22
 sphinx-notfound-page >= 1.0.2
 # For search
 pagefind[bin] >= 1.5.0