[.NET] Use collection expressions in docs

As of C# 12 we can now use collection expressions to reduce some boilerplate when initializing collections.

doc/classes/PackedByteArray.xml

@@ -369,7 +369,7 @@
 				print(array.hex_encode()) # Prints: 0b2eff
 				[/gdscript]
 				[csharp]
-				var array = new byte[] {11, 46, 255};
+				byte[] array = [11, 46, 255];
 				GD.Print(array.HexEncode()); // Prints: 0b2eff
 				[/csharp]
 				[/codeblocks]