Fix oauth2 helper user step typing (#50618)

homeassistant/helpers/config_entry_oauth2_flow.py

@@ -316,7 +316,11 @@ class AbstractOAuth2FlowHandler(config_entries.ConfigFlow, metaclass=ABCMeta):
         """
         return self.async_create_entry(title=self.flow_impl.name, data=data)
 
-    async_step_user = async_step_pick_implementation
+    async def async_step_user(
+        self, user_input: dict[str, Any] | None = None
+    ) -> FlowResult:
+        """Handle a flow start."""
+        return await self.async_step_pick_implementation(user_input)
 
     @classmethod
     def async_register_implementation(