fix: bug in extra repr in fixed unpooling module

Author: okunator

cellseg_models_pytorch/modules/upsample/fixed_unpool.py

@@ -43,4 +43,4 @@ def forward(self, x: torch.Tensor) -> torch.Tensor:
 
     def extra_repr(self):
         """Print output."""
-        return "scale_factor={self.scale_factor}"  # .format(**self.__dict__)
+        return f"scale_factor={self.scale_factor}"  # .format(**self.__dict__)