tests: fix memory leak in timertest cancellation test
tests: fix memory leak in timertest cancellation test

acbellini/seastar,acbellini/seastar,scylladb/scylla-seastar,scylladb/scylla-seastar,dreamsxin/seastar,acbellini/seastar,sjperkins/seastar,kjniemi/seastar,printedheart/seastar,printedheart/seastar,scylladb/scylla-seastar,sjperkins/seastar,scylladb/seastar,kjniemi/seastar,dreamsxin/seastar,scylladb/seastar,sjperkins/seastar,printedheart/seastar,syuu1228/seastar,cloudius-systems/seastar,cloudius-systems/seastar,syuu1228/seastar,avikivity/seastar,dreamsxin/seastar,scylladb/seastar,kjniemi/seastar,avikivity/seastar,avikivity/seastar,cloudius-systems/seastar,syuu1228/seastar