Add __code__ to types.MethodType (#12749)

Author: Avasam

stdlib/@tests/stubtest_allowlists/common.txt

@@ -494,6 +494,7 @@ typing(_extensions)?\.TextIO\.newlines
 typing(_extensions)?\.(Async)?ContextManager
 
 types.MethodType.__closure__  # read-only but not actually a property; stubtest thinks it doesn't exist.
+types.MethodType.__code__  # read-only but not actually a property; stubtest thinks it doesn't exist.
 types.MethodType.__defaults__  # read-only but not actually a property; stubtest thinks it doesn't exist.
 types.ModuleType.__dict__  # read-only but not actually a property; stubtest thinks it's a mutable attribute.
 types.ModuleType.__getattr__  # this doesn't exist at runtime

stdlib/types.pyi

@@ -424,6 +424,8 @@ class MethodType:
     @property
     def __closure__(self) -> tuple[CellType, ...] | None: ...  # inherited from the added function
     @property
+    def __code__(self) -> CodeType: ...  # inherited from the added function
+    @property
     def __defaults__(self) -> tuple[Any, ...] | None: ...  # inherited from the added function
     @property
     def __func__(self) -> Callable[..., Any]: ...