Fixes an intermittent failure caused by a race condition with background
gossip messages.
Previously Eve's `RefsAnnounced` message could be processed by Bob
after the test updated the identity document to include Alice-Laptop
as a delegate. This caused Bob to unexpectedly fetch the issue in the
background, failing the `!has_issue` assertion.
We now explicitly wait for Bob to receive Eve's announcement before
updating the identity document.
bdd991a5f1