pytype: ignore some signature mismatch in configitems

pytype is grumpy about the dict.update having a more complex signature than the
one we use here.

pytype error:

  itemregister: Overriding method signature mismatch [signature-mismatch]
    Base signature: 'def builtins.dict.update(self) -> None'.
    Subclass signature: 'def itemregister.update(self, other) -> Any'.
    Parameter 'other' must have a default value.

mercurial/configitems.py

@@ -82,7 +82,7 b' class itemregister(dict):'
         super(itemregister, self).__init__()
         self._generics = set()
 
-    def update(self, other):
+    def update(self, other):  # pytype: disable=signature-mismatch
         super(itemregister, self).update(other)
         self._generics.update(other._generics)