[feat] #71 삭제 가능 여부 예외 메세지 추가

src/main/java/org/gachon/checkmate/domain/scrap/service/ScrapService.java

@@ -85,7 +85,7 @@ private void validateDuplicateScrap(Long postId, Long userId) {
 
     private void validateExistScrap(Long postId, Long userId) {
         if(!existPostInScrap(postId, userId))
-            throw new InvalidValueException();
+            throw new InvalidValueException(INVALID_DELETE_SCRAP);
     }
 
     private boolean existPostInScrap(Long postId, Long userId) {