pytype: ignore some signature mismatch in registrar

pytype is grumpy about a sub method having a different signature than the one we
use here.

pytype error:

  internalmerge: Overriding method signature mismatch [signature-mismatch]
    Base signature: 'def _funcregistrarbase._extrasetup(self, name, func) -> Any'.
    Subclass signature: 'def internalmerge._extrasetup(self, name, func, mergetype, onfailure = None, precheck = None, binary = False, symlink = False) -> Any'.
    Parameter 'mergetype' must have a default value.

mercurial/registrar.py

@@ -524,7 +524,7 b' class internalmerge(_funcregistrarbase):'
         precheck=None,
         binary=False,
         symlink=False,
-    ):
+    ):  # pytype: disable=signature-mismatch
         func.mergetype = mergetype
         func.onfailure = onfailure
         func.precheck = precheck