Rollup merge of #88911 - FabianWolff:issue-88653, r=petrochenkov

Improve error message for type mismatch in generator arguments

Fixes #88653. The code example given there is invalid because the `Generator` trait (unlike the `Fn` traits) does not take the generator arguments in tupled-up form (because there can only be one argument, from my understanding). Hence, the type error in the example in #88653 is correct, because the given generator takes a `bool` argument, whereas the function's return type talks about a generator with a `(bool,)` argument.

The error message is both confusing and wrong, though: It is wrong because it displays the wrong "expected signature", and it is confusing because both the "expected" and "found" notes point at the same span. With my changes, I get the following, more helpful output:
```
error[E0631]: type mismatch in generator arguments
 --> test.rs:5:22
  |
5 | fn foo(bar: bool) -> impl Generator<(bool,)> {
  |                      ^^^^^^^^^^^^^^^^^^^^^^^ expected signature of `fn((bool,)) -> _`
6 |     |bar| {
  |     ----- found signature of `fn(bool) -> _`
```

0 files changed, 0 insertions, 0 deletions