fix bug : config_file type str -> Path

[CorentinSeznec]

Fix bug for Titan inference. Cast config_file as a Path instead of a str as intended for from_json argument. Command: python bin/inference.py --model_path /scratch/shared/py4cast/logs/camp0/titan/halfunet/sezn_run_dev_41 --date 2023010300 --dataset titan --infer_steps 2

Stack trace: Traceback (most recent call last): File "/home/mrmn/seznecc/repository/py4cast/bin/inference.py", line 71, in dm = PlDataModule( File "", line 10, in init File "/home/mrmn/seznecc/repository/py4cast/py4cast/lightning.py", line 63, in post_init self.train_ds, self.val_ds, self.test_ds = get_datasets( File "/home/mrmn/seznecc/repository/py4cast/py4cast/datasets/init__.py", line 95, in get_datasets return dataset_kls.from_json( File "/home/mrmn/seznecc/repository/py4cast/py4cast/datasets/titan/init__.py", line 699, in from_json fname.stem, AttributeError: 'str' object has no attribute 'stem