input: Write a python function to generate a 5x5 matrix of random integers between 0 and 4 using numpy.
  assert random_matrix().shape == (5, 5)
  assert (random_matrix() >= 0).all() and (random_matrix() < 5).all()
  assert isinstance(random_matrix(), np.ndarray)
output: def random_matrix():
      import numpy as np
      return np.random.randint(0, 5, size=(5, 5))