asset: add more test cases for ExternalKey.PubKey #3654

Job	Run time
Format check	20s
cross compilation	5m 7s
Docker build check	3m 50s
Compilation check	55s
run itests	10m 59s
Lint check	2m 43s
run itests postgres	19m 18s
migration version check	11s
go mod check	24s
RPC check	1m 15s
run LiT tests	47s
sample configuration check	40s
Sqlc check	2m 45s
test vector check	1m 15s
run unit tests (unit-race)	12m 14s
run unit tests (unit-cover)	3m 21s
run unit tests (unit dbbackend=postgres)	6m 23s
finish	3s
	1h 12m 30s

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