test: fix TEST-10-ISSUE-2467

test: fix TEST-10-ISSUE-2467

Depending on the timing, socat will either get ECONNREFUSED oder EPIPE
from systemd. The latter will cause it to exit(1) and subsequently the
test to fail.
We are not actually interested in the return code of socat though. The
test is supposed to check, whether rate limiting of a socket unit works
properly.

So ignore any failures from the socat invocation and instead check, if
test10.socket is in state "failed" with result "trigger-limit-hit" after
it has been triggered.

TriggerLimitIntervalSec= by default is set to 2s. A "sleep 10" should
give systemd enough time even on slower machines, to reach the trigger
limit.

For better readability, break the test into separate ExecStart lines.

Fixes #19154.