Fix mypy variable conflict.

Author: busykoala

sqlmodel/main.py

@@ -619,12 +619,12 @@ def _calculate_keys(
             # if include_relations is set in the Config for a model
             # Otherwise do not include relationships as that would easily lead
             # to infinite recursion, or traversing the whole database
-            keys = set(self.__fields__.keys())
+            model_keys = set(self.__fields__.keys())
             include_relations = getattr(self.Config(), "include_relations", {})
             for relation_key in self.__sqlmodel_relationships__.keys():
                 if relation_key in include_relations:
-                    keys.add(relation_key)
-            return keys
+                    model_keys.add(relation_key)
+            return model_keys
 
         keys: AbstractSet[str]
         if exclude_unset: