Conditionally disabled custom 404 pages on dev docs (#11596)

This is for testing error pages more in production and can be reverted later.

docs/conf.py

@@ -21,7 +21,8 @@
     "hoverxref.extension",
     "multiproject",
     "myst_parser",
-    "notfound.extension",
+    # For testing, conditionally disable the custom 404 pages on dev docs
+    # "notfound.extension",
     "sphinx_copybutton",
     "sphinx_design",
     "sphinx_tabs.tabs",
@@ -55,6 +56,10 @@
 
 docset = get_project(multiproject_projects)
 
+# Disable custom 404 on dev docs
+if docset == "user":
+    extensions.append("notfound.extension")
+
 ogp_site_name = "Read the Docs Documentation"
 ogp_use_first_image = True  # https://github.com/readthedocs/blog/pull/118
 ogp_image = "https://docs.readthedocs.io/en/latest/_static/img/logo-opengraph.png"