tapdb: fixes another issue with the syncer cache #3810

Job	Run time
Compilation check	1m 38s
Docker build check	4m 5s
cross compilation	12m 2s
Format check	20s
run itests	11m 56s
run itests postgres	20m 20s
Lint check	2m 49s
migration version check	11s
go mod check	19s
RPC check	1m 17s
run LiT tests	16m 49s
sample configuration check	39s
Sqlc check	2m 52s
test vector check	56s
run unit tests (unit-race)	14m 55s
run unit tests (unit-cover)	4m 38s
run unit tests (unit dbbackend=postgres)	6m 30s
finish	3s
	1h 42m 19s

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