chgserver: mark as a built-in extension

hgext/chgserver.py

@@ -48,6 +48,12 b' from mercurial import ('
     util,
 )
 
+# Note for extension authors: ONLY specify testedwith = 'internal' for
+# extensions which SHIP WITH MERCURIAL. Non-mainline extensions should
+# be specifying the version(s) of Mercurial they are tested with, or
+# leave the attribute unspecified.
+testedwith = 'internal'
+
 _log = commandserver.log
 
 # copied from hgext/pager.py:uisetup()