Incompatible return type error doesn't quote types

[nematsakis]

The error message for an incompatible return type doesn't have quotation marks around the types. This makes it difficult to programmatically process the output of mypy to filter "expected" errors.

Example output:
Error: Incompatible return value type (got List[Type1], expected List[Type2])

Expected output:
Error: Incompatible return value type (got "List[Type1]", expected "List[Type2]")

[ilevkivskyi]

We actually have a PR #3430 for this, but it looks like @mistermocha is currently busy.
I think this is essentially a duplicate of #3409

[OddBloke]

I believe this was fixed in #3873.