Hot-fix FreeCommand ignoring messages from guild

After updating to JDA5, GuildMessageReceviedEvent was removed.
MessageReceivedEvent has to be used instead.

To "counter" this, one can use the isFromGuild method.

I use this method, but incorrect.
I should invert the if statemen; if the message is NOT from a guild, ignore.

This modification fixes the update that broke the help system.

application/src/main/java/org/togetherjava/tjbot/commands/free/FreeCommand.java

@@ -295,7 +295,7 @@ public void onEvent(@NotNull GenericEvent event) {
         if (event instanceof ReadyEvent readyEvent) {
             onReady(readyEvent);
         } else if (event instanceof MessageReceivedEvent messageEvent) {
-            if (messageEvent.isFromGuild()) {
+            if (!messageEvent.isFromGuild()) {
                 return;
             }