Set PXAT timedelta is flaky

[chayim]

@skip_if_server_version_lt('6.2.0')
def test_set_pxat_timedelta(self, r):
    expire_at = redis_server_time(r) + datetime.timedelta(seconds=10)
    assert r.set('a', '1', pxat=expire_at)

  assert 0 < r.ttl('a') <= 10

E AssertionError: assert 11 <= 10
E + where 11 = <bound method Commands.ttl of Redis<ConnectionPool<Connection<host=master,port=6379,db=9>>>>('a')
E + where <bound method Commands.ttl of Redis<ConnectionPool<Connection<host=master,port=6379,db=9>>>> = Redis<ConnectionPool<Connection<host=master,port=6379,db=9>>>.t

[chayim]

@AvitalFineRedis