Avoid Sphinx 5.1.0.

HexDecimal · HexDecimal · commit 79c8e382f53e · 2022-07-25T14:39:23.000-07:00
This version has a regression.
diff --git a/docs/requirements.txt b/docs/requirements.txt
@@ -1,2 +1,2 @@
-sphinx>=4.2
+sphinx>=5.0.2,!=5.1.0
 sphinx_rtd_theme
