go.mod: bump lnd@v0.20.0-beta and taproot-assets #2750

Job	Run time
run unit tests	18m 53s
go mod check	11m 35s
SQL compilation check	9s
verify that auto-generated documentation is up-to-date	3m 37s
build and lint code	8m 6s
RPC compilation check	1m 50s
	44m 10s

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