devel: use the new 'config' argument of the develwarn in deprecwarn

Controling all deprecation warnings with the same config seems sensible. This
mirror a fix (about missing gating) submitted for stable but with the new API.

mercurial/ui.py

@@ -1169,7 +1169,7 b' class ui(object):'
             return
         msg += ("\n(compatibility will be dropped after Mercurial-%s,"
                 " update your code.)") % version
-        self.develwarn(msg, stacklevel=2)
+        self.develwarn(msg, stacklevel=2, config='deprec-warn')
 
 class paths(dict):
     """Represents a collection of paths and their configs.