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

Reproduce the report with mypy 1.10.1 on Python 3.12.1 using the shown returns_none function and assertion. Trace the func-returns-value diagnostic, then verify that assertions about callables annotated to return None produce no complaint while the existing diagnostic remains for inappropriate value use.