Bug when using --validate flag

[lcadalzo]

When using the --validate flag, I get the following error:

Traceback (most recent call last):
File "/opt/conda/lib/python3.9/runpy.py", line 197, in _run_module_as_main
return _run_code(code, main_globals, None,
File "/opt/conda/lib/python3.9/runpy.py", line 87, in _run_code
exec(code, run_globals)
File "/workspace/armory/scenarios/main.py", line 226, in <module>
run_validation(args.config, args.from_file)
File "/workspace/armory/scenarios/main.py", line 98, in run_validation
with test_path_context as test_path:
File "/opt/conda/lib/python3.9/contextlib.py", line 119, in __enter__
return next(self.gen)
File "/opt/conda/lib/python3.9/importlib/resources.py", line 175, in _path_from_reader
opener_reader = reader.open_resource(norm_resource)
File "<frozen importlib._bootstrap_external>", line 1055, in open_resource
IsADirectoryError: [Errno 21] Is a directory: '/workspace/armory/validation/test_config

I'm running the following command from the rc0.16.1 branch:

python -m armory run scenario_configs/mnist_baseline.json --validate