update_bond: TxDescriptor<{
    new_deposit: bigint;
}>

Update the candidacy bond of collator candidate origin to a new amount new_deposit.

Setting a new_deposit that is lower than the current deposit while origin is occupying a top-DesiredCandidates slot is not allowed.

This call will fail if origin is not a collator candidate, the updated bond is lower than the minimum candidacy bond, and/or the amount cannot be reserved.