Fix the Delta.Method enums to inherit str, so the string comparison w…

…orks

This fix directly affects the permissions check for role reporter, which
were failing before, as `delta.method == Delta.Method.Create` was
returning false.

docker-app/qfieldcloud/core/models.py

@@ -1067,7 +1067,7 @@ def clean(self) -> None:
 
 
 class Delta(models.Model):
-    class Method(Enum):
+    class Method(str, Enum):
         Create = "create"
         Delete = "delete"
         Patch = "patch"