Three example test drivers call driver.close() without await in tearDownAll(), silently dropping the Future<void>. This means the WebDriver connection is never reliably closed before the test process exits.

Affected files:

• examples/hello_world/test_driver/smoke_web_engine_test.dart:28
• examples/platform_channel/test_driver/button_tap_test.dart:17
• examples/platform_channel_swift/test_driver/button_tap_test.dart:17

Root cause: PR #181513 systematically fixed unawaited FlutterDriver.close() callsites across packages/, dev/, and test/, but examples/ was not included in the sweep.

Fix: Add await to each driver.close() call. One-line change per file.