CI test import/test_fast_slow_import sometime fail

[progier389]

Issue Description

CI test_fast_slow_import sometime fails with:

  assert total_time1 < total_time2

E assert 2.2014029026031494 < 2.1553120613098145

We should at least mark it as flaky
note: The db size (1K users) is now far too small to provide reliable result but I do not think it is worth to try fix the test
(disable it is enough) as using private memory in import is an obscure feature specific to obsolete bdb database.