Fix build failed of Settings test cases while importing AndroidX

- API change in AndroidX Preference causes a build breakage
- Apply explicit casting for the new API interface

Test: robotest
Fixes: 121109361
Change-Id: If3e7be9e53c7860252523700d6721ae4956db68a

tests/robotests/src/com/android/settings/connecteddevice/ConnectedDeviceGroupControllerTest.java

@@ -100,7 +100,8 @@ public class ConnectedDeviceGroupControllerTest {
         mConnectedDeviceGroupController.onDeviceAdded(mPreference);
 
         assertThat(mPreferenceGroup.isVisible()).isTrue();
-        assertThat(mPreferenceGroup.findPreference(PREFERENCE_KEY_1)).isEqualTo(mPreference);
+        assertThat((Preference) mPreferenceGroup.findPreference(PREFERENCE_KEY_1))
+                .isEqualTo(mPreference);
     }
 
     @Test