fix queue converter singleton initialization (#56081)

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Collection/QueueOfTConverter.cs

@@ -10,7 +10,7 @@ internal sealed class QueueOfTConverter<TCollection, TElement>
         where TCollection : Queue<TElement>
     {
         /// <summary>Lazily initialized singleton for hardcoding by the IAsyncEnumerable streaming deserializer.</summary>
-        internal static QueueOfTConverter<TCollection, TElement> Instance = _instance ??= new();
+        internal static QueueOfTConverter<TCollection, TElement> Instance => _instance ??= new();
         private static QueueOfTConverter<TCollection, TElement>? _instance;
 
         protected override void Add(in TElement value, ref ReadStack state)