Make sure the tests start with the same seed for reproducibility

tests/test_for_r_and_python_concordance.py

@@ -29,6 +29,9 @@
 Now, we perform unit tests on the MR-link-2 functions. to ensure that there is no creep of the 
 First function v0
 """
+
+np.random.seed(42)
+
 def test_mr_link2_loglik_reference_v0_basic_r_concordance():
     th = np.array([0.1, 0.01, 0.01])
     lam = np.array([1, 2, 3])