Typeshed in mypy 1.14.0 prohibits using `email.policy.default` with `email.message_from_string()`

[jwodder]

(I'm not sure whether this is a mypy bug or a typeshed bug, but the mypy issue template says that problems with specific functions should be reported here, so ...)

Consider the following code:

from email import message_from_string, policy

with open("message.eml") as fp:
    source = fp.read()

msg = message_from_string(source, policy=policy.default)

I think it's clear that this code should be acceptable, but running mypy 1.14.0 on this produces the following error:

email-policy.py:6: error: Argument "policy" to "message_from_string" has incompatible type "EmailPolicy[EmailMessage]"; expected "Policy[Message[str, str]]"  [arg-type]