Fix some NRT on StringCollections (#106116)

Co-authored-by: Eirik Tsarpalis <[email protected]>

Author: lilinus

src/libraries/System.Collections.Specialized/ref/System.Collections.Specialized.cs

@@ -213,10 +213,10 @@ public StringCollection() { }
         bool System.Collections.IList.IsReadOnly { get { throw null; } }
         object? System.Collections.IList.this[int index] { get { throw null; } set { } }
         public int Add(string? value) { throw null; }
-        public void AddRange(string[] value) { }
+        public void AddRange(string?[] value) { }
         public void Clear() { }
         public bool Contains(string? value) { throw null; }
-        public void CopyTo(string[] array, int index) { }
+        public void CopyTo(string?[] array, int index) { }
         public System.Collections.Specialized.StringEnumerator GetEnumerator() { throw null; }
         public int IndexOf(string? value) { throw null; }
         public void Insert(int index, string? value) { }

src/libraries/System.Collections.Specialized/src/System/Collections/Specialized/StringCollection.cs

@@ -69,7 +69,7 @@ public int Add(string? value)
         /// <devdoc>
         /// <para>Copies the elements of a string array to the end of the <see cref='System.Collections.Specialized.StringCollection'/>.</para>
         /// </devdoc>
-        public void AddRange(string[] value)
+        public void AddRange(string?[] value)
         {
             ArgumentNullException.ThrowIfNull(value);
 
@@ -99,7 +99,7 @@ public bool Contains(string? value)
         /// <para>Copies the <see cref='System.Collections.Specialized.StringCollection'/> values to a one-dimensional <see cref='System.Array'/> instance at the
         ///    specified index.</para>
         /// </devdoc>
-        public void CopyTo(string[] array, int index)
+        public void CopyTo(string?[] array, int index)
         {
             data.CopyTo(array, index);
         }