False positive Lint/UselessAssign

[Blacksmoke16]

hash = {"foo" => "bar"}

def call(v)
end

unless v = hash["foo"]?
  call v = "default"
end

v

Results in:

[W] Lint/UselessAssign: Useless assignment to variable `v`
> unless v = hash["foo"]?

The assignment is for sure not useless as it handles assigning v if that key is present in the hash, otherwise is assigned within the unless block.

Creating a new issue as unlike #447, this doesn't require any type declarations or macros.