input: Write a function to generate numbers starting from 0 up to a limit with a step of 4 and return them as a list.
  assert generate_numbers(20) == [0, 4, 8, 12, 16]
  assert generate_numbers(15) == [0, 4, 8, 12]
  assert generate_numbers(10) == [0, 4, 8]
output: def generate_numbers(limit):
      return list(range(0, limit, 4))