Core/CreatureGroups: Don't set positionZ to ground for flying creatures.

(cherry picked from commit df4c856360a56c3abe1c231ed37cd3673515c090)

src/server/game/Entities/Creature/CreatureGroups.cpp

@@ -240,6 +240,7 @@ void CreatureGroup::LeaderMoveTo(float x, float y, float z)
         Trinity::NormalizeMapCoord(dx);
         Trinity::NormalizeMapCoord(dy);
 
+        if (!member->IsFlying())
             member->UpdateGroundPositionZ(dx, dy, dz);
 
         if (member->IsWithinDist(m_leader, dist + MAX_DESYNC))