e2e: improve flake in missing_delegate_default_branch — heartwood

The missing_delegate_default_branch test was flakey and would fail checking if Bob had the rid in storage.

This can be improved by waiting to ensure that Bob has a RefsFetched event before performing the check.

     let mut bob = bob.spawn();
     let mut seed = seed.spawn();
     let bob_events = bob.handle.events();
     alice.handle.seed(rid, Scope::All).unwrap();
     bob.handle.seed(rid, Scope::All).unwrap();
     seed.handle.seed(rid, Scope::All).unwrap();

     bob.connect(&seed);
     bob.handle.fetch(rid, seed.id, DEFAULT_TIMEOUT).unwrap();
     bob_events
         .wait(
             |e| {
                 matches!(e, service::Event::RefsFetched { updated, .. } if !updated.is_empty())
                     .then_some(())
             },
             DEFAULT_TIMEOUT,
         )
         .unwrap();
     assert!(bob.storage.contains(&rid).unwrap());
     // Helper to assert that Bob's default branch is not in storage

             &radicle::cob::issue::TYPENAME,
             &issue,
         );
         assert!(repo.backend.find_reference(issue_ref.as_str()).is_ok());
         assert!(repo.backend.find_reference(issue_ref.as_str()).is_ok(),);
     };
     // The seed fetches from Bob and checks that: