New parser deviates from old parser in edge cases with function type comments

[ilevkivskyi]

This is a follow-up for #21823. Most notably we get a false negative in situations like this:

class A:
    def f(self):
        # type: () -> None
        def g(x):
            # type: () -> None  # Error not detected: signature has too few parameters
            pass

cc @JukkaL