Fixup: do not call Tick::shutdown if it is already shutdown #3085

Job	Run time
openraft-test (stable, 0)	2m 57s
openraft-test (nightly, 30)	3m 13s
openraft-test (nightly, 0, single-term-leader)	3m 1s
external-stores (stores/rocksstore-v2)	6m 1s
openraft-feature-test (nightly)	49s
cluster-benchmark (cluster_benchmark)	45s
openraft-feature-test (nightly, serde)	51s
openraft-feature-test (nightly, single-term-leader)	49s
openraft-test-bench (nightly)	52s
openraft-feature-test (nightly, single-term-leader,serde,singlethreaded)	51s
stores (memstore)	52s
Build (nightly, bench,serde,bt,singlethreaded)	47s
stores (rocksstore)	5m 57s
stores (rocksstore-compat07)	6m 3s
stores (sledstore)	1m 5s
examples (stable, raft-kv-memstore)	2m 23s
examples (stable, raft-kv-memstore-singlethreaded)	54s
examples (stable, raft-kv-rocksdb)	8m 9s
examples (nightly, raft-kv-memstore)	2m 4s
examples (nightly, raft-kv-memstore-singlethreaded)	1m 16s
examples (nightly, raft-kv-rocksdb)	6m 36s
lint	6m 30s
tests-feature-test (nightly)	2m 49s
tests-feature-test (nightly, single-term-leader)	2m 51s
tests-feature-test (nightly, loosen-follower-log-revert)	2m 47s
	1h 11m 12s

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