fuzz: cover deferred writing in chanmon_consistency #23371

Job	Run time
benchmark	18m 19s
ext-test	6m 14s
check_docs	8m 10s
fuzz_sanity	13m 38s
tor-connect	5m 58s
check_release	3m 5s
fuzz	1h 0m 35s
build-cfg-flags / build (self-hosted, 1.75.0)	18m 49s
build-sync / build (self-hosted, 1.75.0)	26m 47s
rustfmt	17s
build-nostd / build (self-hosted, 1.75.0)	21m 49s
build-bindings / build (self-hosted, 1.75.0)	22m 36s
linting	2m 21s
build-workspace / build (self-hosted, 1.75.0)	14m 36s
build-features / build (self-hosted, 1.75.0)	29m 39s
coverage	23m 25s
notify-failure	0s
	4h 36m 18s

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