Let CI only check changed files

[SataQiu]

升级 circleci ，仅检查变更的 markdown 文件

暂时将 spell check 设置为弱检查（只检查，不阻止合并），因为很多单词不在术语表中。 最棘手的是，每篇文章都有原作者信息，人名往往不是标准单词，不能每篇文章都修改 .spelling 文件。

/cc @rootsongjc @haiker2011

[auto-comment[bot]]

Thank you for raising the pull request. We will review it as soon as possible. To ensure document quality, we have enabled the CI test, which currently includes spell and format checks. If your pull request fails to pass the spell check, but you are sure that the word(s) is/are correct, feel free to add the word(s) into our glossary .spelling. :laughing:

[haiker2011]

/lgtm