I tried to use an action space tuple of 2 discrete actions

```
ACTION_SPACE = gym.spaces.Tuple([
gym.spaces.Discrete(3),
gym.spaces.Discrete(3),
])
```

then got this error:

```
ValueError: The two structures don't have the same nested structure.
First structure: type=tuple str=(0,)
Second structure: type=tuple str=(Discrete(3), Discrete(3))
More specifically: The two structures don't have the same number of elements. First structure: type=tuple str=(0,). Second structure: type=tuple str=(Discrete(3), Discrete(3))
Entire first structure:
(.,)
Entire second structure:
(., .)
```

If I change action space to:

```
ACTION_SPACE = gym.spaces.Tuple([
gym.spaces.Discrete(3),
])
```

then it runs without errors

Sorry this isnâ€™t an reproducible script, I would like to confirm whether QMIX algorithm work with more than 1 discrete action. If so, is there an example of it? the two_step_game example uses 1 discrete action