Fix ViewPager2IdlingResource to unregister IdlingResource

Bug: 218806007
Test: atest com.android.providers.media.photopicker.espresso
Change-Id: I8570818850680da295cdf8cc0ab58256483f4b78
diff --git a/tests/src/com/android/providers/media/photopicker/espresso/ViewPager2IdlingResource.java b/tests/src/com/android/providers/media/photopicker/espresso/ViewPager2IdlingResource.java
index 1063561..f3b6d86 100644
--- a/tests/src/com/android/providers/media/photopicker/espresso/ViewPager2IdlingResource.java
+++ b/tests/src/com/android/providers/media/photopicker/espresso/ViewPager2IdlingResource.java
@@ -51,7 +51,7 @@
 
     @Override
     public void close() throws Exception {
-        IdlingRegistry.getInstance().register(this);
+        IdlingRegistry.getInstance().unregister(this);
     }
 
     private final class IdleStateListener extends ViewPager2.OnPageChangeCallback {