`service::users::Data::list_local_users` is possibly bugged

https://gitlab.computer.surgery/matrix/grapevine/-/blob/5a490a4397f0c6a36dab1cb631dadc67a849deab/src/database/key_value/users.rs#L102-115

The comment says:

A user account is considered "local" if the length of it's password is greater then zero.

But this is technically wrong because the admin bot (usually) has its password unset (i.e. is zero bytes long).