Warning reported for assignment to property marked [AllowNull]

[cston]

No warnings should be reported:

#nullable enable

using System.Diagnostics.CodeAnalysis;

class C<T>
{
    [MaybeNull, AllowNull]
    T F = default;
    [MaybeNull, AllowNull]
    T P { get; } = default; // warning CS8601: Possible null reference assignment

    C([AllowNull]T t)
    {
        F = t;
        P = t; // warning CS8601: Possible null reference assignment
    }
}

See also #39922.