extensions: ignore "sub-options" when looking for extensions config suboptions are separated by ":" (see the path one for example). So we dont want to confuse these config with actual extensions. We don't have extensions sub option yet, but I am about to introduce one for making sure an extensions can load. So lets level the floor first. Differential Revision: https://phab.mercurial-scm.org/D11819

--- a/mercurial/configitems.py	Tue Nov 23 17:52:38 2021 -0800
+++ b/mercurial/configitems.py	Fri Nov 26 16:51:58 2021 +0100
@@ -1281,7 +1281,7 @@
 )
 coreconfigitem(
     b'extensions',
-    b'.*',
+    b'[^:]*',
     default=None,
     generic=True,
 )