input: Write a python function to add two matrices using numpy.
  assert np.array_equal(add_matrices(np.array([[2, 3], [1, 4]]), np.array([[5, 6], [7, 8]])), np.array([[7, 9], [8, 12]]))
  assert np.array_equal(add_matrices(np.array([[1, 2], [3, 4]]), np.array([[5, 6], [7, 8]])), np.array([[6, 8], [10, 12]]))
  assert np.array_equal(add_matrices(np.array([[0, 0], [0, 0]]), np.array([[0, 0], [0, 0]])), np.array([[0, 0], [0, 0]]))
output: import numpy as np
  
  def add_matrices(mat1, mat2):
      return np.add(mat1, mat2)