input: Write a python function to check if a given 3x3 matrix is empty (all elements are zero).
  assert is_empty_matrix([[0, 0, 0], [0, 0, 0], [0, 0, 0]]) == True
  assert is_empty_matrix([[1, 0, 0], [0, 0, 0], [0, 0, 0]]) == False
  assert is_empty_matrix([[0, 0, 0], [0, 1, 0], [0, 0, 0]]) == False
output: def is_empty_matrix(matrix):
      for row in matrix:
          for element in row:
              if element != 0:
                  return False
      return True