[hotfix] 페이징 중복 문제 해결, countDistinct

* findAllByBoardIdAndGroupCodeAndMemberCode 메소드는 현재 프론트에서 쓰지 않는 메소드이기는 하지만, 함께 수정함(같은 로직이기 때문에)

src/main/java/ussum/homepage/infra/jpa/post/PostRepositoryImpl.java

@@ -210,14 +210,13 @@ public Page<Post> findAllByBoardIdAndGroupCodeAndMemberCode(Long boardId, GroupC
                 .fetch();
 
         JPAQuery<Long> countQuery = queryFactory
-                .select(postEntity.count())
+                .select(postEntity.countDistinct())
                 .from(postEntity)
                 .leftJoin(postEntity.userEntity, userEntity)
                 .leftJoin(memberEntity).on(memberEntity.userEntity.eq(userEntity))
                 .leftJoin(memberEntity.groupEntity, groupEntity)
                 .leftJoin(postFileEntity).on(postFileEntity.postEntity.eq(postEntity))
-                .where(whereClause)
-                .distinct();
+                .where(whereClause);
 
         return PageableExecutionUtils.getPage(
                 content.stream().map(postMapper::toDomain).collect(Collectors.toList()),