input: Write a function to fit a linear regression model using the given numpy code.
  assert np.allclose(fit_linear_regression([1, 2, 3], [3, 6, 9]), np.array([0., 3.]))
  assert np.allclose(fit_linear_regression([1, 4, 5], [2, 8, 10]), np.array([0.66666667, 1.86666667]))
  assert np.allclose(fit_linear_regression([2, 3, 5], [5, 7, 11]), np.array([2.8, 1.2]))
output: import numpy as np
  
  def fit_linear_regression(x, y):
      X = np.vstack([np.ones(len(x)), x]).T
      Y = np.array(y)
      beta = np.linalg.inv(X.T @ X) @ X.T @ Y
      return beta