CI: add GCC 11
CI: add GCC 11

newsboat/newsboat,newsboat/newsboat,der-lyse/newsboat,der-lyse/newsboat,der-lyse/newsboat,newsboat/newsboat,der-lyse/newsboat,der-lyse/newsboat,newsboat/newsboat,der-lyse/newsboat,newsboat/newsboat,newsboat/newsboat,newsboat/newsboat,der-lyse/newsboat,newsboat/newsboat,der-lyse/newsboat