Pin Sphinx version to 6.2.1

Signed-off-by: Jono Yang <jyang@nexb.com>

Author: JonoYang

setup.cfg

@@ -58,6 +58,6 @@ testing =
     isort
 
 docs =
-    Sphinx >= 3.3.1
+    Sphinx == 6.2.1
     sphinx-rtd-theme >= 0.5.0
     doc8 >= 0.8.1