Bash completion: Does not handle sub-commands with hyphens

The bash completion doesn't handle subcommands that have hyphens in them correctly.

**ArgumentParser version:** `1.5.0` and main
**Swift version:** N/A

### Checklist
- [x] If possible, I've reproduced the issue using the `main` branch of this package
- [x] I've searched for [existing GitHub issues](https://github.com/apple/swift-argument-parser/issues)

### Steps to Reproduce
The unit tests have a subcommand and the generated bash completion doesn't actually work. So the tests already reproduce the issue if the bash completion is loaded.

### Expected behavior
Subcommand completion should be correct.

### Actual behavior
```
_base_test_sub-command: command not found
```

Start with the unit tests mentioned in the issue and load their generated Bash completion to reproduce the `_base_test_sub-command: command not found` error. Trace the completion generation for hyphenated subcommands, then verify that completing such a subcommand works correctly without the command-not-found error.

Written by the indexing model from the issue text.