The command order of prepare-docs is incorrect.
We should prepare same version with different locale at once, otherwise the doc files for `zh-cn` in `i18n` folder will be incorrect.
Before: (files in current is as same as version 1.19)

After:

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Reviewed-on: https://gitea.com/gitea/gitea-docusaurus/pulls/92
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Reviewed-by: silverwind <silverwind@noreply.gitea.com>
Co-authored-by: yp05327 <576951401@qq.com>
Co-committed-by: yp05327 <576951401@qq.com>