Error while running obstacle avoidance script for turtlebot3 in ROS2

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Hello, I am trying to run an obstacle avoidance script and test it in gazebo simulation using turtlebot 3 in ROS2 but I am getting the following error - [WARN] [1667317780.806097773] [obstacle_avoidance]: New publisher discovered on topic '/scan', offering incompatible QoS. No messages will be received from it. Last incompatible policy:RELIABILITY Please help me in solving this issue, thank you.

Here is the code I have written -

import rclpy 
from rclpy.node import Node 
from sensor_msgs.msg import LaserScan 
from geometry_msgs.msg import Twist

    distToObstacle = 1

    class ObstacleAvoidance(Node):
        def __init__(self):
            super().__init__('obstacle_avoidance')
            self.sub = self.create_subscription(LaserScan, '/scan', self.obstacle_callback, 10)
            self.pub = self.create_publisher(Twist, '/cmd_vel', 10)

        def obstacle_callback(self, msg):
            self.get_logger().info('The distance to obstacle is %s ' % msg.ranges[300])

            move = Twist()

            if msg.ranges[300] > distToObstacle:
                move.linear.x = 0.5
                move.angular.z = 0.0

            if msg.ranges[300] <= distToObstacle:
                move.linear.x = 0.5
                move.angular.z = 1.5 

            self.pub.publish(move)

    def main(args=None):

        rclpy.init(args=args)

        obstacle_avoidance = ObstacleAvoidance()

        rclpy.spin(obstacle_avoidance)

        obstacle_avoidance.destroy_node()

        rclpy.shutdown()

    if __name__ == '__main__':
        main()