Fix new_callable overload

Author: srittau

src/pytest_mock/plugin.py

@@ -286,6 +286,20 @@ def __call__(
         ) -> _T:
             ...
 
+        @overload
+        def __call__(
+            self,
+            target: str,
+            new: None,
+            spec: Optional[builtins.object],
+            create: bool,
+            spec_set: Optional[builtins.object],
+            autospec: Optional[builtins.object],
+            new_callable: Callable[[], _T],
+            **kwargs: Any
+        ) -> _T:
+            ...
+
         @overload
         def __call__(
             self,
@@ -295,7 +309,8 @@ def __call__(
             create: bool = ...,
             spec_set: Optional[builtins.object] = ...,
             autospec: Optional[builtins.object] = ...,
-            new_callable: Callable[[], _T] = ...,
+            *,
+            new_callable: Callable[[], _T],
             **kwargs: Any
         ) -> _T:
             ...