input: Write a python function to check if a list contains a specific number.
  assert contains_number([1, 2, 3, 4, 5], 3) == True
  assert contains_number([1, 2, 3, 4, 5], 6) == False
  assert contains_number([10, 20, 30, 40, 50], 30) == True
output: def contains_number(lst, num):
      return num in lst