auto-t: fix failed_roam_test to pass when run on its own

When running this test with others the hostapd neighbors are already
grouped which lets the test pass. On its own this does not happen
and it fails.

autotests/testPSK-roam/failed_roam_test.py

@@ -221,6 +221,8 @@ class Test(unittest.TestCase):
         cls.rule_bss2 = hwsim.rules.create()
         cls.rule_bss2.source = hwsim.get_radio('rad2').addresses[0]
 
+        HostapdCLI.group_neighbors(*cls.bss_hostapd)
+
     @classmethod
     def tearDownClass(cls):
         IWD.clear_storage()