go.mod: update lndclient to v0.20.0-4 #2713

Job	Run time
SQL compilation check	10s
verify that auto-generated documentation is up-to-date	3m 28s
RPC compilation check	1m 33s
go mod check	11m 31s
run unit tests	9m 38s
build and lint code	8m 0s
run unit tests	18m 47s
go mod check	11m 31s
build and lint code	8m 0s
SQL compilation check	10s
verify that auto-generated documentation is up-to-date	3m 28s
RPC compilation check	1m 33s
	1h 17m 49s

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