add check to silence false positive lint warning

The BootReceiver class is explicitly not exported.

app/src/main/java/app/attestation/auditor/BootReceiver.java

@@ -7,6 +7,9 @@
 public class BootReceiver extends BroadcastReceiver {
     @Override
     public void onReceive(final Context context, final Intent intent) {
+        if (!Intent.ACTION_BOOT_COMPLETED.equals(intent.getAction())) {
+            throw new IllegalStateException("invalid action");
+        }
         RemoteVerifyJob.restore(context);
     }
 }