wrong/unsound type for `path-has-extension?`

This program typechecks, but shouldn't, because `x` is `#true`:
```racket
#lang typed/racket
(define x : (U Bytes False)
  (path-has-extension? "a.git" ".git"))
```

The type of `path-has-extension?` is currently:
```racket
(-> (U Path-For-Some-System Path-String) (U Bytes String) (U Bytes False))
```
but the result type should actually be `Boolean`, the same as the documented contract.