Run executor until parked at end of each iteration of random collaboration test

Without this, the server doesn't get dropped at the end of the test, and we eventually run
out of file handles due to sqlite connections being retained.

crates/collab/src/tests/randomized_integration_tests.rs

@@ -152,6 +152,8 @@ async fn test_random_collaboration(
             drop(client);
         });
     }
+
+    deterministic.run_until_parked();
 }
 
 fn on_failure() {