`closed=True` should not be supported for Python <3.15

Bug Report

mypy accepts closed=True on TypedDicts before Python 3.15. I think this should be allowed in typing-only files, but not at runtime.

To Reproduce

from typing import TypedDict

class A(TypedDict, closed=True):
    x: int

a: A = {"x": 5, "y": "5"}  # E

Expected Behavior

An error when defining A.

Actual Behavior

No error when defining A.

Your Environment

Reproduced in mypy-play.

• Mypy version used: 2.3.0
• Mypy command-line flags: N/A
• Mypy configuration options from mypy.ini (and other config files): N/A
• Python version used: 3.12

Start with the mypy-play reproduction using a TypedDict and closed=True under Python 3.12, then trace how mypy handles this argument and Python-version checks. Done means closed=True is rejected for Python versions before 3.15 while remaining accepted in typing-only files, with regression coverage for the reported behavior.