TEST-04-JOURNAL: add one more missing journalctl --sync

TEST-04-JOURNAL: add one more missing journalctl --sync

Fixes the following failure:
```
TEST-04-JOURNAL.sh[124]: + add_logs_filtering_override delegated-cgroup-filtering.service 01-discard-hello '~hello'
TEST-04-JOURNAL.sh[124]: + local unit=delegated-cgroup-filtering.service
TEST-04-JOURNAL.sh[124]: + local override_name=01-discard-hello
TEST-04-JOURNAL.sh[124]: + local 'log_filter=~hello'
TEST-04-JOURNAL.sh[124]: + mkdir -p /run/systemd/system/delegated-cgroup-filtering.service.d/
TEST-04-JOURNAL.sh[124]: + echo -ne '[Service]\nLogFilterPatterns=~hello'
TEST-04-JOURNAL.sh[124]: + NEEDS_RELOAD=1
TEST-04-JOURNAL.sh[1408]: ++ run_service_and_fetch_logs delegated-cgroup-filtering.service
TEST-04-JOURNAL.sh[1408]: ++ local unit=delegated-cgroup-filtering.service
TEST-04-JOURNAL.sh[1408]: ++ [[ -n 1 ]]
TEST-04-JOURNAL.sh[1408]: ++ systemctl daemon-reload
TEST-04-JOURNAL.sh[1408]: ++ NEEDS_RELOAD=
TEST-04-JOURNAL.sh[1408]: ++ systemctl start delegated-cgroup-filtering.service
TEST-04-JOURNAL.sh[1408]: ++ journalctl --sync
TEST-04-JOURNAL.sh[1408]: ++ journalctl -q -u delegated-cgroup-filtering.service -I -p notice
TEST-04-JOURNAL.sh[124]: + [[ -z Jul 28 22:41:41 H delegated_cgroup_filtering_payload.sh[1448]: child_process: hello, world!
TEST-04-JOURNAL.sh[124]: Jul 28 22:41:41 H delegated_cgroup_filtering_payload.sh[1448]: child_process: hello, people! ]]
TEST-04-JOURNAL.sh[124]: + at_exit
```