FIX: user 관심 category 수정 기능 에러 픽스

<footer>
- 해결: #176

src/main/java/com/example/betteriter/fo_domain/mypage/service/MypageService.java

@@ -139,6 +139,6 @@ private void checkUploadProfileImageRequestValidation(MultipartFile image) {
     }
 
 	public void updateUserCategory(Users user, MypageRequest.UpdateCategoryRequest request) {
-	    user.setUsersCategory(request.getCategories());
+        userService.updateUserCategory(user, request.getCategories());
     }
 }

src/main/java/com/example/betteriter/fo_domain/user/service/UserService.java

@@ -9,6 +9,7 @@
 import com.example.betteriter.fo_domain.user.repository.UsersRepository;
 import com.example.betteriter.fo_domain.user.repository.UsersWithdrawReasonRepository;
 import com.example.betteriter.global.common.code.status.ErrorStatus;
+import com.example.betteriter.global.constant.Category;
 import com.example.betteriter.global.util.RedisUtil;
 import com.example.betteriter.global.util.SecurityUtil;
 import com.example.betteriter.infra.s3.S3Service;
@@ -17,9 +18,9 @@
 import lombok.extern.slf4j.Slf4j;
 import org.springframework.stereotype.Service;
 import org.springframework.transaction.annotation.Transactional;
-import org.springframework.web.multipart.MultipartFile;
 
 import java.util.Arrays;
+import java.util.List;
 import java.util.stream.Collectors;
 
 /**
@@ -104,4 +105,9 @@ public Users getUserByEmail(String email) {
     public void updateUserDetail(UsersDetail detail) {
         this.userDetailRepository.save(detail);
     }
+
+    public void updateUserCategory(Users user, List<Category> categories) {
+        user.setUsersCategory(categories);
+        this.usersRepository.save(user);
+    }
 }