test(be): 트랜잭션 어노테이션 삭제

Author: ki-met-hoon

src/backend/chat_server/src/main/java/com/jootalkpia/chat_server/service/ChatService.java

@@ -32,7 +32,6 @@ public class ChatService {
     private final FileRepository fileRepository;
     private final SnowflakeIdGenerator snowflakeIdGenerator;
 
-    @Transactional
     public void processChatMessage(ChatMessageRequest request, Long channelId) {
         CommonResponse commonData = createCommonData(request.userId(), channelId);
         List<MessageResponse> messageData = createMessageData(request.content(), request.attachmentList());