test: Update FCMConfig.java

src/main/java/ewha/lux/once/global/config/FCMConfig.java

@@ -17,7 +17,7 @@
 public class FCMConfig {
     @Bean
     FirebaseMessaging firebaseMessaging() throws IOException {
-        ClassPathResource resource = new ClassPathResource("firebase/once-firebase-adminsdk.json");
+        ClassPathResource resource = new ClassPathResource("src/main/resources/firebase/once-firebase-adminsdk.json");
 
         InputStream refreshToken = resource.getInputStream();