docs: fix duplicate form text in toggle button (#1508)

# docs: fix duplicate form text in toggle button

`synchronizing-with-effects.md` 문서의 예제 토글 버튼 텍스트에서 중복된 `form`을 제거했습니다.

- 변경 전: `form 보기 form`, `form 숨기기 form`
- 변경 후: `form 보기`, `form 숨기기`

<img width="985" height="525" alt="image"
src="https://github.com/user-attachments/assets/80c52a93-d544-4e89-804a-3650fe298cca"
/>
<img width="979" height="519" alt="image"
src="https://github.com/user-attachments/assets/d656db13-1aea-45c7-ba2d-873a20157298"
/>


## 필수 확인 사항

- [x] [기여자 행동 강령 규약<sup>Code of
Conduct</sup>](https://github.com/reactjs/ko.react.dev/blob/main/CODE_OF_CONDUCT.md)
- [x] [기여
가이드라인<sup>Contributing</sup>](https://github.com/reactjs/ko.react.dev/blob/main/CONTRIBUTING.md)
- [x] [공통 스타일 가이드<sup>Universal Style
Guide</sup>](https://github.com/reactjs/ko.react.dev/blob/main/wiki/universal-style-guide.md)
- [x] [번역을 위한 모범 사례<sup>Best Practices for
Translation</sup>](https://github.com/reactjs/ko.react.dev/blob/main/wiki/best-practices-for-translation.md)
- [x] [번역 용어 정리<sup>Translate
Glossary</sup>](https://github.com/reactjs/ko.react.dev/blob/main/wiki/translate-glossary.md)
- [x] [`textlint` 가이드<sup>Textlint
Guide</sup>](https://github.com/reactjs/ko.react.dev/blob/main/wiki/textlint-guide.md)
- [x] [맞춤법 검사<sup>Spelling
Check</sup>](https://nara-speller.co.kr/speller/)

## 선택 확인 사항

- [ ] 번역 초안 작성<sup>Draft Translation</sup>
- [ ] 리뷰 반영<sup>Resolve Reviews</sup>

Author: goodsmell

src/content/learn/synchronizing-with-effects.md

@@ -1112,7 +1112,7 @@ export default function Form() {
   const [upper, setUpper] = useState(false);
   return (
     <>
-      <button onClick={() => setShow(s => !s)}>form {show ? '숨기기' : '보기'} form</button>
+      <button onClick={() => setShow(s => !s)}>form {show ? '숨기기' : '보기'}</button>
       <br />
       <hr />
       {show && (