[IMP] test_mail: follow activities in performance tests

Commit 07ae0ccc4e set activities as not followed by default on records.
However this has an impact on performance test that should not happen.
Indeed performance tests should be based on technical decisions, not business
decisions. We therefore set activities as followed by default in some advanced
performance tests to always have results that can be compared.

addons/test_mail/tests/test_performance.py

@@ -143,6 +143,9 @@ class TestAdvMailPerformance(TransactionCase):
             'groups_id': [(6, 0, [self.env.ref('base.group_user').id])],
         })
 
+        # automatically follow activities, for backward compatibility concerning query count
+        self.env.ref('mail.mt_activities').write({'default': True})
+
     @users('admin', 'emp')
     @warmup
     def test_adv_activity(self):