Cannot assert a callable returns `None` when it must return `None`

Bug Report

mypy prevents you making assertions about callables that must return None when they're called.
This is important as not everyone works in a type-checked context, and so library code must be robust to this.
In my case, I have a chain of callables, the ones in the middle take iterables and return iterables, but the one at the start must take no arguments and the one at the end must consume the upstream iterable and return nothing.

To Reproduce

def returns_none() -> None:
    pass

assert returns_none() is None

Expected Behavior

No mypy complaints

Actual Behavior

"returns_none" does not return a value (it only ever returns None) [func-returns-value]

Your Environment

• Mypy version used: mypy 1.10.1 (compiled: yes)
• Mypy command-line flags: none
• Python version used: Python 3.12.1

使用所示的 returns_none 函数和断言，在 Python 3.12.1 上通过 mypy 1.10.1 重现该报告。跟踪 func-returns-value 诊断，然后验证对于标注为返回 None 的 callable 的断言不会产生任何提示，同时针对不恰当的值使用，现有诊断仍然保留。