Fix type annotation

model.py

@@ -144,7 +144,7 @@ class Model:
 
     def run(self, model_name: str, scheduler_type: str, num_steps: int,
             randomize_seed: bool,
-            seed: int) -> tuple[PIL.Image.Image, int, str | None]:
+            seed: int) -> tuple[PIL.Image.Image, int, str]:
         self.set_pipeline(model_name, scheduler_type)
         if scheduler_type == 'PNDM':
             num_steps = max(4, min(num_steps, 100))