Fix test failure of AvailableMediaDeviceGroupControllerTest

Prevent test failing by avoid using ShadowFragment in the test. This
will cause `androidx.fragment.app.SuperNotCalledException` when creating
HearingAidPairingDialogFragment.

Bug: 299597695
Test: atest AvailableMediaDeviceGroupControllerTest
Change-Id: I99b5213cb78aad97fcb7e44e1babcf6c7f11636e

src/com/android/settings/connecteddevice/AvailableMediaDeviceGroupController.java

@@ -134,6 +134,11 @@ public class AvailableMediaDeviceGroupController extends BasePreferenceControlle
                 AvailableMediaDeviceGroupController.this, fragment.getMetricsCategory());
     }
 
+    @VisibleForTesting
+    public void setFragmentManager(FragmentManager fragmentManager) {
+        mFragmentManager = fragmentManager;
+    }
+
     @VisibleForTesting
     public void setBluetoothDeviceUpdater(BluetoothDeviceUpdater bluetoothDeviceUpdater) {
         mBluetoothDeviceUpdater = bluetoothDeviceUpdater;