fix(test): Use IMPORTANCE_DEFAULT to avoid heads-up dismissal

IMPORTANCE_HIGH shows the notification as a heads-up banner at the
top of the screen. When Maestro swipes down to open the notification
shade, it instead dismisses the heads-up notification, causing it
to disappear entirely. IMPORTANCE_DEFAULT puts the notification
directly in the shade without a heads-up, so the swipe opens the
shade as intended.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: romtsn

sentry-android-integration-tests/sentry-uitest-android-critical/src/main/java/io/sentry/uitest/android/critical/NotificationHelper.kt

@@ -24,7 +24,7 @@ object NotificationHelper {
     if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
       notificationManager.deleteNotificationChannel(CHANNEL_ID)
       val channel =
-        NotificationChannel(CHANNEL_ID, "Notifications", NotificationManager.IMPORTANCE_HIGH)
+        NotificationChannel(CHANNEL_ID, "Notifications", NotificationManager.IMPORTANCE_DEFAULT)
       channel.description = "description"
       notificationManager.createNotificationChannel(channel)
     }