Cannot specify two `file` args

Upfront note: I'm not sure if this issue is on the `mise` or the `usage` side, but I'm leaning `usage`.

I have the following mise task in a file:
```python
#!/usr/bin/env python
#MISE description="Run a comparison of two files"
#USAGE arg ""
#USAGE arg ""

import sys
import pandas as pd

df1 = pd.read_parquet(sys.argv[1])
df2 = pd.read_parquet(sys.argv[2])
```

I want to be able to autocomplete two files when typing the file.
With the above script this works, but I can then never run the task because it always results in an error:
```shellsession
> mise r compare
[compare] ERROR Missing required arg:
Missing required arg:
[compare] ERROR task failed

> mise r compare file1
[compare] ERROR Missing required arg:
[compare] ERROR task failed

> mise r compare file1 file2
[compare] ERROR Missing required arg:
[compare] ERROR task failed
```

If I try to run with no args, I get the error message twice.
But no matter if I run with 1, 2, 3, 5 args, it always shows one error.

If I do
```python
#!/usr/bin/env python
#MISE description="Run a comparison of two files"
#USAGE arg ""
#USAGE arg ""
```
or any other names for the args, I don't get file completion