[scripts] Avoid conflicting type for `pack-next --compress` (#88439)
`type: 'string'` conflicts with `choices: T[]`. It's basically `string |
T` which just collapses to `string` if `T` is a union of string
literals.
Before:
```console
$ p pack-next --help
...
--compress ... [string] [choices: "none", "strip"]
```
After:
```console
$ p pack-next --help
...
--compress ... [choices: "none", "strip"]