Check self permission in BackupManager#isBackupServiceActive

Old method only checked for IPC caller, method isn't an IPC, adding
check for self permission as well.

Bug: 78467264
Test: atest com.google.android.gts.devicepolicy.DeviceOwnerTest#testBackupServiceActive
Change-Id: If9eed90f2deaaf1a4f2376fdf1881e62ee8954fb
1 file changed