Source Obsolete attribute with array named argument doesn't produce diagnostics

[RikkiGibson]

Version Used: 441c154

Steps to Reproduce:

using System;
#pragma warning disable 436

namespace System
{
    public class ObsoleteAttribute : Attribute
    {
        public int[] P1 { get; set; }
    }
}

class C1
{
    [Obsolete(
        P1 = new[] { 0 }
    )]
    void M1() { }
    
    void M2()
    {
        M1(); // expect an obsolete diagnostic here but get none
    }
}

Expected Behavior:
Obsolete diagnostic is issued for call to M1().

Actual Behavior:
No diagnostic is issued.

• If the attribute is modified to not pass an argument for P1, the diagnostic is issued on usage.
• If the attribute is modified to pass a null argument for P1, the diagnostic is issued on usage.
• If the obsoleted member is compiled and referenced from metadata, the diagnostic is issued on usage.