Makes type.__prepare__ a classmethod, also first arg is any (not str), refs #2762

extra_tests/snippets/builtin_type.py

@@ -135,5 +135,8 @@ assert type.__prepare__('name', (bytes, str)) == {}
 assert type.__prepare__(a=1, b=2) == {}
 assert type.__prepare__('name', (object, int), kw=True) == {}
 
+# Previously we needed `name` to be `str`:
+assert type.__prepare__(1) == {}
+
 assert int.__prepare__() == {}
 assert int.__prepare__('name', (object, int), kw=True) == {}

vm/src/builtins/pytype.rs

@@ -343,9 +343,10 @@ impl PyType {
             .insert("__module__".to_owned(), value);
     }
 
-    #[pymethod(magic)]
+    #[pyclassmethod(magic)]
     fn prepare(
-        _name: OptionalArg<PyStrRef>,
+        _cls: PyTypeRef,
+        _name: OptionalArg<PyObjectRef>,
         _bases: OptionalArg<PyObjectRef>,
         _kwargs: KwArgs,
         vm: &VirtualMachine,