Pause bewteen retries in WaitForRepoEmptyState

Forgot a pause, so this was retrying every couple dozen milliseconds,
way too fast.

backend/LexBoxApi/Services/HgService.cs

@@ -293,6 +293,7 @@ public async Task WaitForRepoEmptyState(string code, RepoEmptyState expectedStat
                 RepoEmptyState.Empty => isEmpty,
                 RepoEmptyState.NonEmpty => !isEmpty
             };
+            if (!done) await Task.Delay(650);
         }
     }