Make possible return type in `IOInterface::select()` more explicit (#11171)
Make possible return type in `IOInterface::select()` more explicit (#11171)

`IOInterface::select()` either returns any of `int`, `string`, `bool` or an
array of `string` values. However, since the returned array is always a
list, we can safely change the return type annotation to `list<string>`,
making it more explicit in terms of static code analysis.
composer/composer