Tool may change variables from type `T` to `tuple[T]`

[cmyui]

Hey, I found this while using this as a pre-commit hook (big fan of the the project & your tools btw! :)).

It seems the tool may change turn a type into a tuple[type] in a situation like this;

x = (
    object  # < comma is added here
), object

[asottile]

hideous code, interesting edge case

the code tries to find the first argument to figure out where the tuple parens live (since they're optional) -- but in this case mixes up the (non-existent) outer parens with continuation parens

interestingly enough, the code gets this right in python<3.8 (where the ast offsets of tuples "improved" but also got worse for some cases like this one