Fix incorrect tailwind migration (#30007)

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/**/*
```

templates/repo/commits_list_small.tmpl

@@ -13,7 +13,7 @@
 
 		{{$commitLink:= printf "%s/commit/%s" $.comment.Issue.PullRequest.BaseRepo.Link (PathEscape .ID.String)}}
 
-		<span class="shabox tw-flex tw-content-center tw-float-right">
+		<span class="shabox tw-flex tw-items-center tw-float-right">
 			{{template "repo/commit_statuses" dict "Status" .Status "Statuses" .Statuses}}
 			{{$class := "ui sha label"}}
 			{{if .Signature}}