[scripts.predict] Fix call to 'load_from_checkpoint()'

Since lightning 2.1.0, the error "The classmethod `Pasa.load_from_checkpoint`
cannot be called on an instance." was returned when this method was called,
making the tests fail.

src/ptbench/scripts/predict.py

@@ -134,7 +134,7 @@ def predict(
     datamodule.setup(stage="predict")
 
     logger.info(f"Loading checkpoint from `{weight}`...")
-    model = model.load_from_checkpoint(weight, strict=False)
+    model = type(model).load_from_checkpoint(weight, strict=False)
 
     predictions = run(model, datamodule, DeviceManager(device))