fix(voyager): generate cometbls proofs correctly (#2180)

we were fetching the wrong validators in voyager, where we should have
been fetching H+1 we were fetching H; thus verifying against the
next_validators_hash of the trusted state wasn't working (obviously!)

the fix is adding an increment to the height here:
https://github.com/unionlabs/union/blob/bd86881f9a2768aad1a1a504841e5dc6dd589bd2/lib/relay-message/src/chain/union.rs#L269

which mirrors the traditional tendermint logic as seen here:
https://github.com/unionlabs/union/blob/bd86881f9a2768aad1a1a504841e5dc6dd589bd2/lib/relay-message/src/chain/cosmos.rs#L129