Type argument nullability warning no longer reported for type parameter constrained to 'int?'

[cston]

A warning should be reported for M<T>(t) since T is constrained to int? which does not satisfy the notnull constraint.

#nullable enable
abstract class A<T, U> where T : notnull
{
    internal static void M<V>(V v) where V : T { }
    internal abstract void F<V>(V v) where V : U;
}
class B : A<System.ValueType, int?>
{
    internal override void F<T>(T t)
    {
        M<T>(t);
    }
}

This may be a regression from #45993. Earlier builds reported:

(11,9): warning CS8631: The type 'T' cannot be used as type parameter 'V' in the generic type or method
    'A<ValueType, int?>.M<V>(V)'. Nullability of type argument 'T' doesn't match constraint type 'System.ValueType'.