Invalid nullability mismatch warning on generic notnull ref parameter discard

[jkoritzinsky]

Version Used: 5.6.0-2.26161.119

Steps to Reproduce:

#nullable enable

class Gen<T> where T : notnull
{
    public static void Func(ref T t)
    {
        _ = ref t; // Diagnostic CS8619 here.
    }
}

A minimal repro, with source-code provided, is ideal. Most compiler/language issues can be distilled into a snippet that can be pasted into .NET Lab.

Diagnostic Id: CS8619

Expected Behavior: No diagnostic

Actual Behavior: CS8619: Nullability of reference types in value of type 'T' doesn't match target type 'T?'