Fix flag delete/reset not deleting group flag

Author: APickledWalrus

src/main/java/org/skriptlang/skriptworldguard/elements/expressions/ExprRegionFlag.java

@@ -303,6 +303,11 @@ public void change(Event event, Object @Nullable [] delta, ChangeMode mode) {
 			}
 			case DELETE, RESET -> {
 				for (WorldGuardRegion region : regions) {
+					// first, clear the flag's group flag if possible, then clear the flag itself
+					WorldGuardFlag<?, ?> groupFlag = flag.groupFlag();
+					if (groupFlag != null) {
+						region.region().setFlag(groupFlag.flag(), null);
+					}
 					region.region().setFlag(flag.flag(), null);
 				}
 			}