fn: add synchronous write file #16933

Job	Run time
Sqlc check	2m 47s
RPC and mobile compilation check	1m 45s
check commits	8m 42s
lint code	4m 11s
cross compilation	30m 39s
sample configuration check	30s
run unit tests (btcd unit-cover)	20m 19s
check pinned dependencies (google.golang.org/grpc v1.59.0)	5s
run unit tests (unit tags="kvdb_etcd")	20m 45s
check pinned dependencies (github.com/golang/protobuf v1.5.3)	6s
run unit tests (unit tags="kvdb_postgres")	20m 19s
run ubuntu itests (btcd, backend=btcd cover=1)	30m 1s
run unit tests (unit tags="kvdb_sqlite")	18m 22s
run ubuntu itests (bitcoind, backend=bitcoind cover=1)	38m 24s
run unit tests (btcd unit-race)	40m 3s
run windows itest	7m 15s
run ubuntu itests (bitcoind-notxindex, backend="bitcoind notxindex")	38m 31s
run unit tests (unit-module)	1m 20s
run ubuntu itests (bitcoind-rpcpolling, backend="bitcoind rpcpolling" cover=1)	38m 46s
run ubuntu itests (bitcoind-etcd, backend=bitcoind dbbackend=etcd)	54m 18s
run macOS itest	50m 58s
check release notes updated	12s
run ubuntu itests (bitcoind-postgres, backend=bitcoind dbbackend=postgres)	1h 9m 20s
run ubuntu itests (bitcoind-sqlite, backend=bitcoind dbbackend=sqlite)	41m 58s
run ubuntu itests (bitcoind-postgres-nativesql, backend=bitcoind dbbackend=postgres nativesql=true)	24m 59s
run ubuntu itests (bitcoind-sqlite-nativesql, backend=bitcoind dbbackend=sqlite nativesql=true)	42m 21s
run ubuntu itests (neutrino, backend=neutrino cover=1)	36m 30s
finish	4s
	10h 43m 30s

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