Support more kinds calls to instance_proxy.update

This signature should be more like `dict.update`. This is also needed
for setuptools.

library/builtins.py

@@ -4343,10 +4343,13 @@ def copy(self):
         _instance_guard(instance)
         return {key: _instance_getattr(instance, key) for key in _object_keys(instance)}
 
-    def update(self, d):
+    def update(self, d=_Unbound, /, **kwargs):
         instance = self._instance
         _instance_guard(instance)
-        for key, value in d.items():
+        if d is not _Unbound:
+            for key, value in d.items():
+                _instance_setattr(instance, key, value)
+        for key, value in kwargs.items():
             _instance_setattr(instance, key, value)
 
     def get(self, key, default=None):

library/builtins_test.py

@@ -6898,6 +6898,30 @@ def __init__(self):
         instance.__dict__ = {"hello": "world"}
         self.assertEqual(list(instance.__dict__.keys()), ["hello"])
 
+    def test_vars_update_with_no_args_does_not_raise(self):
+        class C:
+            pass
+
+        instance = C()
+        vars(instance).update()
+
+    def test_vars_update_with_only_kwargs_sets_attribute(self):
+        class C:
+            pass
+
+        instance = C()
+        vars(instance).update(hello=1)
+        self.assertEqual(instance.hello, 1)
+
+    def test_vars_update_with_args_and_kwargs_sets_attributes(self):
+        class C:
+            pass
+
+        instance = C()
+        vars(instance).update({"hello": 1}, world=2)
+        self.assertEqual(instance.hello, 1)
+        self.assertEqual(instance.world, 2)
+
 
 class IsInstanceTests(unittest.TestCase):
     def test_isinstance_with_same_types_returns_true(self):