Parser accepts negative lifetime bounds and interprets as positive bound

[Centril]

The following is accepted by the parser:

fn foo<T: !'static>() {}

and the ! is just silently dropped thus interpreting the constraint as T: 'static.

Regression introduced in #57364 on Feb 24.
cc @estebank @hdhoang

I discovered this while working on a refactoring of parser/ty.rs.
I will fix the issue as part of that refactoring.

[Centril]

Fixed in #67148.