str not compatible with StrOrLiteralStr

Bug Report

mypy doesn't accept str for StrOrLiteralStr

To Reproduce

from string import Formatter
from typing import Iterable, Tuple

class MyFormatter(Formatter):
    def parse(self, s: str) -> Iterable[Tuple[str, str, str, str]]:
        for text, field, spec, conversion in super().parse(s):
            yield "a", "b", "c", "d"

(playground)

Actual Behavior

error: Return type "Iterable[tuple[str, str, str, str]]" of "parse" incompatible with return type "Iterable[tuple[StrOrLiteralStr, StrOrLiteralStr | None, StrOrLiteralStr | None, StrOrLiteralStr | None]]" in supertype "Formatter" [override]

Details

I've asked a question on SO about this and didn't get an answer (yet). As indicated in the comments:

this code passes type checking in mypy 0.971, and fails in mypy 0.981 through 1.5.0

Perhaps it's related to mypy lack of support for LiteralStr #12554

Start with the Formatter.parse override in the Python reproducer and run it in the linked mypy playground, comparing the behavior across the versions mentioned. Trace how mypy handles StrOrLiteralStr and the override return type; done means the reproducer is accepted without incorrectly rejecting str.