test: disable QEMU based testing for TEST-16-EXTEND-TIMEOUT

test: disable QEMU based testing for TEST-16-EXTEND-TIMEOUT

The test is heavily dependent on timeouts, and if we are run in
potentially very slow QEMU instances there's a good chance we'll miss
some which we normally wouldn't miss. Hence, let's test this one in
nspawn only. Given that the test is purely in service management it
shouldn't matter whether it runs in nspawn or qemu, hence keep running
it in nspawn, but don't bother with qemu.

Similar, do this for TEST-03-JOBS, too, which operates with relatively
short sleep times internally.

Fixes: #9123