input: Write a python function to generate a random matrix with values in the range [0, k] of shape (m, n).
  assert generate_matrix(3, 3, 5).shape == (3, 3)
  assert generate_matrix(4, 4, 10).shape == (4, 4)
  assert generate_matrix(2, 5, 7).shape == (2, 5)
output: import numpy as np
  
  def generate_matrix(m, n, k):
      return np.random.randint(0, k + 1, size=(m, n))