Doc: add a space #2725

Job	Run time
cluster-benchmark (cluster_benchmark)	47s
examples (stable, raft-kv-memstore)	2m 11s
examples (stable, raft-kv-rocksdb)	7m 59s
examples (nightly, raft-kv-memstore)	2m 8s
examples (nightly, raft-kv-rocksdb)	19m 58s
external-stores (stores/rocksstore-v2)	5m 58s
lint	6m 35s
openraft-feature-test (nightly)	50s
openraft-feature-test (nightly, serde)	51s
openraft-test (stable, 0)	2m 51s
openraft-test (nightly, 30)	3m 9s
openraft-feature-test (nightly, single-term-leader)	46s
openraft-test (nightly, 0, single-term-leader)	2m 53s
openraft-feature-test (nightly, single-term-leader,serde,singlethreaded)	47s
openraft-test-bench (nightly)	55s
stores (memstore)	41s
stores (rocksstore)	6m 1s
Build (nightly, bench,serde,bt,singlethreaded)	49s
stores (rocksstore-compat07)	6m 13s
stores (sledstore)	50s
tests-feature-test (nightly)	2m 40s
tests-feature-test (nightly, single-term-leader)	2m 44s
tests-feature-test (nightly, loosen-follower-log-revert)	3m 57s
	1h 22m 33s

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