Pin sphinx-book-theme==0.3.3, until we can sort out HTML refactoring.

Author: stevepiercy

requirements.txt

@@ -6,7 +6,7 @@ linkify-it-py
 myst-parser
 pydata-sphinx-theme<=0.8.99  # Build fails in 0.9.0. See https://github.com/plone/documentation/issues/1297
 sphinx-autobuild
-sphinx-book-theme<=0.3.99
+sphinx-book-theme==0.3.3  # Temporary pin until we can sort out HTML refactoring.
 sphinx-copybutton
 sphinx-sitemap
 sphinx-togglebutton