Merge pull request #116 from SW13-Monstera/feat/444

어드민 서술형문제 수정페이지에 "X"가 모범답안으로 추가되는 버그 수정

packages/admin/src/pages/problem/long/LongProblemEditPage.tsx

@@ -87,7 +87,9 @@ export const LongProblemEditPage = () => {
       standardAnswers:
         Array.from(
           document.getElementsByClassName('standard-answer') as HTMLCollectionOf<HTMLInputElement>,
-        ).map((e) => e.value) || [],
+        )
+          .filter((e) => !e.ariaHidden)
+          .map((e) => e.value) || [],
       tags: tagState.filter((tag) => tag.isChecked).map((e) => e.id),
       gradingStandards: [
         ...keywordStandardState.map(({ content, score, type }) => {