Bump docutils from 0.20.1 to 0.21.2 in /docs (#4342)

docs/requirements.txt

@@ -3,7 +3,7 @@
 myst-parser==4.0.0
 Sphinx==7.4.7
 # Older versions break Sphinx even though they're declared to be supported.
-docutils==0.20.1
+docutils==0.21.2
 sphinxcontrib-programoutput==0.17
 sphinx_copybutton==0.5.2
 furo==2024.8.6