input: Write a function to calculate the roots of a quadratic equation using numpy.
  assert np.allclose(quadratic_roots(1, -6, 9), [3, 3])
  assert np.allclose(quadratic_roots(1, -3, 2), [2, 1])
  assert np.allclose(quadratic_roots(1, -2, 1), [1, 1])
output: def quadratic_roots(a, b, c):
      import numpy as np
      coefficients = [a, b, c]
      roots = np.roots(coefficients)
      return roots