build(admob): update core peer dependency to v8.4.0 [publish]

Author: Salakar

packages/admob/package.json

@@ -27,7 +27,7 @@
     "ad consent"
   ],
   "peerDependencies": {
-    "@react-native-firebase/app": "8.3.1"
+    "@react-native-firebase/app": "8.4.0"
   },
   "publishConfig": {
     "access": "public"