chainntnfs: fix test `testSingleConfirmationNotification` #17052

Job	Run time
RPC and mobile compilation check	1m 58s
check commits	9m 18s
lint code	3m 51s
cross compilation (i386, freebsd-386 linux-386 windows-386)	7m 1s
sample configuration check	6m 21s
cross compilation (amd64, darwin-amd64 freebsd-amd64 linux-amd64 netbsd-amd64 openbsd-amd64 windo...	15m 6s
Sqlc check	6m 44s
cross compilation (arm, darwin-arm64 freebsd-arm linux-armv6 linux-armv7 linux-arm64 windows-arm)	14m 10s
check pinned dependencies (google.golang.org/grpc v1.59.0)	5s
run ubuntu itests	0s
check pinned dependencies (github.com/golang/protobuf v1.5.3)	3s
run unit tests (btcd unit-cover)	19m 37s
run unit tests (unit tags="kvdb_etcd")	20m 33s
run windows itest	0s
run unit tests (unit tags="kvdb_postgres")	19m 28s
run macOS itest	0s
run unit tests (unit tags="kvdb_sqlite")	18m 57s
run unit tests (btcd unit-race)	40m 2s
check release notes updated	0s
run unit tests (unit-module)	1m 9s
finish	6s
	3h 4m 29s

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