Katalon Studio itself uses SLF4J and Logback library. This means that you can not control those library for yourself, as KS holds control over them.
I once did a research trying to configure the logging behavior of KS runtime:
My conclusion was: my code can not control the logging behavior of KS runtime at all because KS does not let me do it.
I would suggest to you that you should avoid using Logback in your code; rather you shoud use KeywordUtil#loginfo(String) or System.out.println instead. If you stick to the idea of using Logback directly as you want to, you would waste your time as KS would not let you do it.