Replace "<input>" to "<textarea>" in Copyable

[shanhuhai]

replace "" to "" in Copyable , fix the issue of can not copy Line breaks in "data-content"</p> </div> </div> <div class="page-bar-simple"> </div> <div class="footer"> <ul class="body"> <li>© <script> document.write(new Date().getFullYear()) </script> Githubissues.</li> <li>Githubissues is a development platform for aggregating issues.</li> </ul> </div> <script src="https://cdn.jsdelivr.net/npm/jquery@3.5.1/dist/jquery.min.js"></script> <script src="/githubissues/assets/js.js"></script> <script src="/githubissues/assets/markdown.js"></script> <script src="https://cdn.jsdelivr.net/gh/highlightjs/cdn-release@11.4.0/build/highlight.min.js"></script> <script src="https://cdn.jsdelivr.net/gh/highlightjs/cdn-release@11.4.0/build/languages/go.min.js"></script> <script> hljs.highlightAll(); </script> </body> </html>