inner class of NamedTuple triggers "Invalid statement"

This will show an error.

from typing import NamedTuple


class Name(NamedTuple):
    name: str = ""

    class Inner:
        pass

>>> error: Invalid statement in NamedTuple definition; expected "field_name: field_type [= default]"

However, this works fine:

class Name:
    name: str = ""

    class Inner:
        pass

mypy 0.761
Python 3.8.5 (default, Jan 27 2021, 15:41:15)
[GCC 9.3.0] on linux

Reproduce the reported case using the NamedTuple definition with a nested Inner class, then trace the NamedTuple definition handling that emits the "Invalid statement" diagnostic. Compare it with the ordinary class example; done means the nested class is accepted without that diagnostic while existing field validation remains intact.