bus-unit-util: extend the bus call timeout for UnitFreezer

bus-unit-util: extend the bus call timeout for UnitFreezer

Follow-up for 1d617b35fef5f7783287965f766c8bb85e932b8e.
Should fix https://github.com/systemd/systemd/issues/33269.

From the logs in the bug:
Jun 10 22:55:37 systemd-logind[909]: The system will suspend now!
Jun 10 22:55:37 ModemManager[996]: <msg> [sleep-monitor-systemd] system is about to suspend
...
Jun 10 22:55:48 systemd-sleep[422408]: Failed to freeze unit 'user.slice': Connection timed out
Jun 10 22:55:48 systemd-sleep[422408]: Performing sleep operation 'suspend'...

The delay is ~11 s, consistent with the patch that set the timeout to 10 s.
Looks like this is not enough. It's the freeze operation that fails, but
thawing might be slow too, so just bump the timeout again.