This waits until a tx has likely been confirmed, before trying to send
the next one, because nonce management is broken in the ethers.js
wallet and it tries to replace a previous tx if two are sent quickly in
succession.
This will most likely break, when there are multiple independent
contrbution issuance calls (e.g. two PRs merged quickly in succession).
But at least it fixes issues/PRs with multiple assignees for most cases.
