input: Write a python function to create a class Vehicle with methods to increase and decrease speed.
  assert isinstance(v := Vehicle(5, 20), Vehicle)
  assert v.speed == 20
  v.increase_speed()
  assert v.speed == 30
  v.decrease_speed()
  assert v.speed == 20
  v.decrease_speed()
  assert v.speed == 10
output: class Vehicle:
      def __init__(self, increment, speed):
          self.increment = increment
          self.speed = speed
  
      def increase_speed(self):
          self.speed += self.increment
  
      def decrease_speed(self):
          self.speed -= self.increment