Flow typing doesn't infer generic arguments

Bug Report

I think the following should type check, but mypy errors on the last line. It's unable to infer that matching on the type of x.inner means we know that we have a Foo[str] and not a Foo[int].

#!/usr/bin/env python

from typing import *

T = TypeVar('T')

class Foo(Generic[T]):
    def __init__(self, inner: T) -> None:
        self.inner = inner

def foo(x: Foo[int] | Foo[str]) -> Foo[str]:
    match x.inner:
        case int():
            raise Exception("Unsupported")
        case str():
            return x # error: Incompatible return value type (got "Foo[int] | Foo[str]", expected "Foo[str]")  [return-value]

To Reproduce

Gist URL: https://gist.github.com/mypy-play/2be996e76f0d979d32be113f891803ed
Playground URL: https://mypy-play.net/?mypy=latest&python=3.12&gist=2be996e76f0d979d32be113f891803ed

Expected Behavior

It should type check :)

Actual Behavior

error: Incompatible return value type (got "Foo[int] | Foo[str]", expected "Foo[str]")  [return-value]

Your Environment

• Mypy version used: mypy 1.10.0 (compiled: yes)
• Mypy command-line flags: `--strict``
• Mypy configuration options from mypy.ini (and other config files): N/A
• Python version used: 3.12

Inizia eseguendo il reproducer fornito per Python 3.12 con mypy 1.10.0 e --strict, usando il gist o il playground collegato. Traccia il comportamento del flow typing intorno al match su x.inner e verifica che l’esempio restituisca Foo[str] senza l’errore di ritorno incompatibile.