input: Write a function to calculate the approximate value of pi using the given numba-accelerated function.
  assert round(calculate_pi(), 2) == 500999.83
  assert round(calculate_pi(), 1) == 500999.8
  assert isinstance(calculate_pi(), float)
output: from numba import jit
  
  @jit(nopython=True)
  def approximate_pi():
      total = 0
      for k in range(1, 1000000):
          total += 1 / k**2
      return (total * 6)**0.5
  
  def calculate_pi():
      return approximate_pi()