util: fix the signature for the pypy override of sortdict.update()

PyCharm flagged this as not matching the base class signature.  Not sure if
there was anything supplying these extra arguments though.

Differential Revision: https://phab.mercurial-scm.org/D10275

mercurial/util.py

@@ -1296,11 +1296,13 b' class sortdict(collections.OrderedDict):'
 
     if pycompat.ispypy:
         # __setitem__() isn't called as of PyPy 5.8.0
-        def update(self, src):
+        def update(self, src, **f):
             if isinstance(src, dict):
                 src = pycompat.iteritems(src)
             for k, v in src:
                 self[k] = v
+            for k in f:
+                self[k] = f[k]
 
     def insert(self, position, key, value):
         for (i, (k, v)) in enumerate(list(self.items())):