Fix wrong event type

Event type was changed from 'onchange' to 'change'. This led change in
waiting for event. Which solved the problem that 'continuous' posture
had to be the first posture.

device-posture/device-posture-change-event.https.html

@@ -8,11 +8,13 @@
 
 // REFERENCE https://source.chromium.org/chromium/chromium/src/+/main:third_party/blink/web_tests/http/tests/inspector-protocol/device-posture/device-posture-change-event.js
 promise_test(async (t) => {
-  const watcher = new EventWatcher(t, navigator.devicePosture, ['onchange']);
-  const postures = ['continuous', 'folded', 'continuous', 'folded'];
+  const watcher = new EventWatcher(t, navigator.devicePosture, ['change']);
+  const postures = ['folded', 'continuous', 'folded'];
   for (const posture of postures) {
-    await test_driver.set_device_posture(posture);
-    await watcher;
+    await Promise.all([
+      watcher.wait_for('change'),
+      test_driver.set_device_posture(posture)
+    ]);
     assert_equals(posture, navigator.devicePosture.type);
   }
 }, 'Device posture test: device-posture-change-event.js.');