This updates the type signature for `#scan_repositories` to address a
runtime type error and to reflect the actual return type.
The logic in `#scan_repositories` to check for unsupported
repositories leads to a type error, as `#ofail` has a void return
type. To resolve this, I moved the repository verification code into
`#run` (after `repos` is defined but before it's used) and used
`#odie`, so the command will exit early with an error.
While I was at it, I updated the type for the `repos` parameter to
not be `nilable`, as it shouldn't be `nil` based on how we're
handling `repos` in `#run`.
403b0bf3f1