Add unrecognized event type

https://github.com/SteamRE/SteamKit/issues/493

ArchiSteamFarm/ArchiHandler.cs

@@ -292,6 +292,7 @@ namespace ArchiSteamFarm {
 			internal enum ENotification : byte {
 				Unknown = 0,
 				Trading = 1,
+				Unknown10 = 10, // TODO: This was mentioned as a possibility by one user, but I didn't check yet what 10 stands for
 
 				// Only custom below, different than ones available as user_notification_type
 				Items = 255

ArchiSteamFarm/Bot.cs

@@ -2070,6 +2070,9 @@ namespace ArchiSteamFarm {
 							Trading.OnNewTrade().Forget();
 						}
 
+						break;
+					// Notifications we're not really interested in, but still valid
+					case ArchiHandler.NotificationsCallback.ENotification.Unknown10:
 						break;
 					default:
 						ASF.ArchiLogger.LogGenericWarning(string.Format(Strings.WarningUnknownValuePleaseReport, nameof(notification.Key), notification.Key));