Inaccurate error with different types in PHPDoc and typehint

[orklah]

This fixes #6128

After running the snippet in the original issue, we now get this result:

ERROR: MismatchingDocblockReturnType - sandbox.php:4:12 - Docblock has incorrect return type 'string', should be 'int|null' (see https://psalm.dev/142)

• @return string

ERROR: InvalidReturnType - sandbox.php:4:12 - The declared return type 'string' for getInt is incorrect, got 'int|null' (see https://psalm.dev/011)

• @return string

The MismatchingDocblockReturnType is indeed fixed. Note that a new error is emitted that basically sees the error from another point of view. Not sure if that's expected. EDIT: I believe it's expected. I tried and when there are three different types (signature + docblock + code), the two errors are consistent so it's not just a duplicate

I also fixed a bug I made in ReturnTypeCollector a few months ago that was messing with the second error

I didn't add test because it's changing wording and I don't think we already have tests that do so.

[weirdan]

Thanks!