[rel-db] Uncomment threading test

[vkrasnovyd]

Test: ./tests/system/action/motion/test_create_sequential_number.py: test_create_sequential_numbers_race_condition.

Seems to run into an infinite loop even with consistent data. After force stop the next attempt to run any other test fails with the logs:

These lines are repeted many times:

SQL statement "INSERT INTO truncate_tables (tablename) VALUES (composed_name) ON CONFLICT (tablename) DO NOTHING"
PL/pgSQL function store_table_names() line 5 at SQL statement

After them these are printed once:

SQL statement "INSERT INTO os_notify_log_t (operation, fqid, xact_id, timestamp) VALUES (operation, fqid, pg_current_xact_id(), 'now')"
PL/pgSQL function log_modified_models() line 14 at SQL statement