Issue with running train_trials.py due to unsupported 'gym.spaces.dict.Dict'

stable-baselines3 does not support '<class 'gym.spaces.dict.Dict'>',  so when I run trials/scripts/train_trials.py, I get the following error
```
assert not hasattr(obs_space, "spaces"), f"Unsupported structured space '{type(obs_space)}'"

AssertionError: Unsupported structured space '<class 'gym.spaces.dict.Dict'>
```
How can the code be executed?