Apply suggestions from code review

Author: Borda

src/lightning/pytorch/callbacks/model_checkpoint.py

@@ -611,8 +611,8 @@ def format_checkpoint_name(
         self,
         metrics: dict[str, Tensor],
         filename: Optional[str] = None,
-        prefix: Optional[str] = None,
         ver: Optional[int] = None,
+        prefix: Optional[str] = None,
     ) -> str:
         """Generate a filename according to the defined template.
 
@@ -645,7 +645,7 @@ def format_checkpoint_name(
         """
         filename = filename or self.filename
         filename = self._format_checkpoint_name(
-            filename, metrics, prefix, auto_insert_metric_name=self.auto_insert_metric_name
+            filename, metrics, prefix=prefix, auto_insert_metric_name=self.auto_insert_metric_name
         )
 
         if ver is not None: