Pin Sphinx Sitemap extension (#2227)

An alternative to #2225, addresses sphinx-sitemap issue 109:

- jdillard/sphinx-sitemap#109

Author: gabalafou

pyproject.toml

@@ -57,7 +57,8 @@ doc = [
   "linkify-it-py", # for link shortening
   "rich",
   "sphinxext-rediraffe",
-  "sphinx-sitemap",
+  # TODO: unpin sphinx-sitemap once a solution is offered for https://github.com/jdillard/sphinx-sitemap/issues/109
+  "sphinx-sitemap<2.7.0",
   "sphinx-autoapi>=3.0.0",
   # For examples section
   "myst-parser",