Check List

• I have already read Docs page & Troubleshooting page.
• I have already searched existing issues and they are not help to me.
• I examined error or warning messages and it's difficult to solve.
• I am using the latest version of Hexo. (run hexo version to check)
• My Node.js is matched the required version.

Expected behavior

ref: #5716 (comment)

Since v8.1.0, `<!--test-->` has been incorrectly rendered as <code><!--test--></code>. It should be rendered as <code>&lt;!--test--&gt;</code>.