Use enum

Co-authored-by: Ondrej Baranovič <nulano@nulano.eu>

src/PIL/ImageTransform.py

@@ -20,7 +20,7 @@
 
 
 class Transform(Image.ImageTransformHandler):
-    method: int
+    method: Image.Transform
 
     def __init__(self, data: Sequence[int]) -> None:
         self.data = data