Fix RC Executor annotation (#4395)

Author: vkryachko

firebase-config/src/main/java/com/google/firebase/remoteconfig/RemoteConfigComponent.java

@@ -26,7 +26,7 @@
 import com.google.firebase.FirebaseApp;
 import com.google.firebase.abt.FirebaseABTesting;
 import com.google.firebase.analytics.connector.AnalyticsConnector;
-import com.google.firebase.annotations.concurrent.Background;
+import com.google.firebase.annotations.concurrent.Blocking;
 import com.google.firebase.inject.Provider;
 import com.google.firebase.installations.FirebaseInstallationsApi;
 import com.google.firebase.remoteconfig.internal.ConfigCacheClient;
@@ -88,7 +88,7 @@ public class RemoteConfigComponent {
   /** Firebase Remote Config Component constructor. */
   RemoteConfigComponent(
       Context context,
-      @Background Executor executor,
+      @Blocking Executor executor,
       FirebaseApp firebaseApp,
       FirebaseInstallationsApi firebaseInstallations,
       FirebaseABTesting firebaseAbt,