doc: upgrade sphinx version

Signed-off-by: Andrea Cervesato <andrea.cervesato@suse.com>

Author: acerv

doc/requirements.txt

@@ -1,6 +1,6 @@
 # Use the same sphinx as on readthedocs.org. When updated, make sure
 # sphinx-rtd-theme is compatible with sphinx.
-sphinx==7.2.6
+sphinx==8.2.3
 sphinx-rtd-theme==2.0.0
 myst-parser==4.0.1
 graphviz==0.21