tests: semaphore_test: relax timeouts
tests: semaphore_test: relax timeouts

semaphore_test sometimes fails on loaded machines in the timeout related tests.
This is likely to the timeouts expiring before the code that was supposed to
execute before them actually executed.

Prevent that by increasing the timeouts. The test still runs in ~1.2 seconds.
Message-Id: <8a5690f6aebff609f2e829ed9bd1dd07808ac548@scylladb.com>

scylladb/seastar,scylladb/seastar,syuu1228/seastar,avikivity/seastar,dreamsxin/seastar,dreamsxin/seastar,avikivity/seastar,syuu1228/seastar,cloudius-systems/seastar,avikivity/seastar,dreamsxin/seastar,cloudius-systems/seastar,cloudius-systems/seastar,scylladb/seastar,syuu1228/seastar