Incorrect sig for Relation#select

[donaldong]

https://github.com/chanzuckerberg/redcord/blob/e58e20f4f035ebe910d43cda366c8e0915133f93/lib/redcord/relation.rb#L53

I'd expect this to be an array of symbols (or T.untyped if we don't want to pass in an array but a list of unpacked symbols).