Cover a few more self-referencing cases

src/Compilers/CSharp/Test/Semantic/Semantics/NullableReferenceTypesTests.cs

@@ -7242,13 +7242,19 @@ public void SelfReferencingAttribute()
 using System;
 
 [AttributeUsage(AttributeTargets.All)]
-[ExplicitCrossPackageInternal]
+[ExplicitCrossPackageInternal(ExplicitCrossPackageInternalAttribute.s)]
 internal sealed class ExplicitCrossPackageInternalAttribute : Attribute
 {
-    [ExplicitCrossPackageInternal]
-    internal ExplicitCrossPackageInternalAttribute()
+    internal const string s = """";
+
+    [ExplicitCrossPackageInternal(s)]
+    internal ExplicitCrossPackageInternalAttribute([ExplicitCrossPackageInternal(s)] string prop)
     {
     }
+
+    [return: ExplicitCrossPackageInternal(s)]
+    [ExplicitCrossPackageInternal(s)]
+    internal void Method() { }
 }";
             var comp = CreateNullableCompilation(source);
             comp.VerifyDiagnostics();