channeldb: fix race in TestPackager by removing global test var #14004

Job	Run time
check commits	1m 24s
lint code	3m 46s
cross compilation	9m 58s
sample configuration check	1m 2s
RPC and mobile compilation check	3m 2s
Sqlc check	1m 22s
run unit tests (btcd unit-cover)	14m 35s
run unit tests (unit tags="kvdb_etcd")	18m 18s
run unit tests (unit tags="kvdb_postgres")	18m 14s
check pinned dependencies (google.golang.org/grpc v1.59.0)	4s
run unit tests (unit tags="kvdb_sqlite")	15m 55s
check pinned dependencies (github.com/golang/protobuf v1.5.3)	6s
run macOS itest	55m 5s
run unit tests (btcd unit-race)	34m 0s
run unit tests (unit-module)	1m 1s
run windows itest	40m 27s
run ubuntu itests (btcd, backend=btcd)	36m 14s
check release notes updated	0s
run ubuntu itests (bitcoind, backend=bitcoind)	46m 8s
run ubuntu itests (bitcoind-notxindex, backend="bitcoind notxindex")	45m 57s
run ubuntu itests (bitcoind-rpcpolling, backend="bitcoind rpcpolling")	46m 17s
run ubuntu itests (bitcoind-etcd, backend=bitcoind dbbackend=etcd)	1h 3m 49s
run ubuntu itests (bitcoind-postgres, backend=bitcoind dbbackend=postgres)	1h 19m 50s
run ubuntu itests (bitcoind-sqlite, backend=bitcoind dbbackend=sqlite)	48m 46s
run ubuntu itests (bitcoind-postgres-nativesql, backend=bitcoind dbbackend=postgres nativesql=true)	1h 18m 24s
run ubuntu itests (bitcoind-sqlite-nativesql, backend=bitcoind dbbackend=sqlite nativesql=true)	49m 10s
run ubuntu itests (neutrino, backend=neutrino)	45m 20s
	12h 38m 14s

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