Fix broken e2e test 'test_concurrent_fetches' — heartwood

Previously was asserting over empty sets nullifying its utility (fortunately the behaviour was correct!), updated to clone the HashSets to assert all repositories were fetched by Alice and Bob.

     let scale = config::scale();
     let repos = scale.max(4);
     let limits = Limits {
         // Have one fetch be queued.
         // By setting fetch concurrency to one less than the total number of repos,
         // we guarantee that at least one fetch will be queued while the others
         // are in progress.
         fetch_concurrency: (repos - 1).into(),
         ..Limits::default()
     };

         bob_repos.insert(rid);
     }
     // Clone repositories list for assertions so we don't assert over an empty set.
     let all_alice_repos = alice_repos.clone();
     let all_bob_repos = bob_repos.clone();
     let mut alice = alice.spawn();
     let mut bob = bob.spawn();

     while !bob_repos.is_empty() {
         match alice_events.recv().unwrap() {
             // We're looking for a `RefsFetched` event, which signals a completed fetch.
             // We also ensure that `updated` is not empty, meaning data was actually received.
             Event::RefsFetched { rid, updated, .. } if !updated.is_empty() => {
                 // Once a repo is fetched, remove it from our tracking set.
                 bob_repos.remove(&rid);
                 log::debug!(target: "test", "{} fetched {rid} ({} left)",alice.id, bob_repos.len());
             }

     while !alice_repos.is_empty() {
         match bob_events.recv().unwrap() {
             Event::RefsFetched { rid, updated, .. } if !updated.is_empty() => {
                 // Once a repo is fetched, remove it from our tracking set.
                 alice_repos.remove(&rid);
                 log::debug!(target: "test", "{} fetched {rid} ({} left)", bob.id, alice_repos.len());
             }

         }
     }
     for rid in &bob_repos {
     // Positively assert empty sets, not necessary but proves test was previously broken.
     assert!(bob_repos.is_empty());
     assert!(alice_repos.is_empty());
     for rid in &all_bob_repos {
         let doc = alice
             .storage
             .repository(*rid)

         assert!(proj.name().starts_with("bob"));
     }
     for rid in &alice_repos {
     for rid in &all_alice_repos {
         let doc = bob
             .storage
             .repository(*rid)