message: Use `Realm::Config` for the async open configuration
  Using `ServerTestFile` results in the Realm file being deleted when the
  configuration goes out of scope, completely negating the point of the
  test. This was an oversight introduced while tidying up the test.
diff: @@ -523,7 +523,7 @@ TEST_CASE("Partial sync", "[sync]") {
  // Perform an asynchronous open like bindings do by first opening the Realm without any schema,
  // waiting for the initial download to complete, and then re-opening the Realm with the correct schema.
  {
  - SyncTestFile async_partial_config(partial_config);
  + Realm::Config async_partial_config(partial_config);
  async_partial_config.schema = {};
  async_partial_config.cache = false;
  