Lookahead/parse mismatch: canParseClosureSignature accepts top-level '->' but signature parse fails (missing 'in')

### Issue Kind

Bad Diagnostic Produced

### Source Code

```swift
struct Foo {
func a(s: S [{{g) -> Int {}
}}}
```

### Description

Following #3162, the following code in function [testRecovery141 ](https://github.com/swiftlang/swift-syntax/blob/a113ef952acc8423b91d0d112a84497db6538611/Tests/SwiftParserTest/translated/RecoveryTests.swift#L2427) of [RecoveryTests](https://github.com/swiftlang/swift-syntax/blob/main/Tests/SwiftParserTest/translated/RecoveryTests.swift#L2427) gives the following diagnostics: "expected 'in' in closure signature" at the arrow location, and "unexpected code ') -> Int {}' in closure". However, lookahead shouldn't accept a closure signature here, or the parse should consume consistently, instead of having a mismatch between lookahead and the actual parse.