No warning when overriding method with out T? rather than out T

[cston]

No warnings when compiling:

#nullable enable

abstract class A
{
    public abstract void F<T>(out T t);
}

class B : A
{
    public override void F<T>(out T? t) where T : default { t = default; }
}

Expected: A warning for B.F<T>():

(10,26): warning CS8765: Nullability of type of parameter 't' doesn't match overridden member

[RikkiGibson]

The root cause could be similar to #49071

[alrz]

out T? and out T wont warn for partial either, so it's probably the exact same issue.

[alrz]

We permit covariant nullables for output types, out and partial return type would be an exception..

[RikkiGibson]

These signatures appears to be contravariant (override signature accepts a less specific type, which is only safe for inputs).