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/**/*
```

(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

templates/user/settings/security/openid.tmpl

@@ -7,7 +7,7 @@
 			{{ctx.Locale.Tr "settings.openid_desc"}}
 		</div>
 		{{range .OpenIDs}}
-			<div class="flex-item tw-content-center">
+			<div class="flex-item tw-items-center">
 				<div class="flex-item-leading">
 					{{svg "fontawesome-openid" 20}}
 				</div>