Fixes https://github.com/go-gitea/gitea/issues/30005. Regression from
https://github.com/go-gitea/gitea/pull/29945.
There was only once instance of `tw-content-center` before that PR, so I
just ran below command and reverted that one instance.
```sh
perl -p -i -e 's#tw-content-center#tw-items-center#g' web_src/js/**/* templates/**/* models/**/* tests/**/*
```
(cherry picked from commit 04f9ad056882fc3f21b247b16f84437adf0f36d8)
Conflicts:
templates/repo/diff/conversation.tmpl
templates/repo/header.tmpl
templates/repo/issue/filter_list.tmpl
templates/repo/issue/view_content/conversation.tmpl
templates/repo/wiki/view.tmpl
web_src/js/components/DashboardRepoList.vue
re-ran the command after discarding the Gitea changes to
ensure all Forgejo files are also covered
3ea7437fa6