gtk: Fix BitsetIter test

As the iter is expected to be valid

Author: bilelmoussaoui

gtk4/src/bitset_iter.rs

@@ -161,7 +161,5 @@ mod tests {
         assert_eq!(iter.previous(), Some(0));
         assert_eq!(iter.previous(), None);
         assert!(!iter.is_valid());
-        assert_eq!(iter.next(), Some(1));
-        assert!(iter.is_valid());
     }
 }