Center-aligning content of WebAuthN page (#21127)

<!--

Please check the following:

1. Make sure you are targeting the `main` branch, pull requests on
release branches are only allowed for bug fixes.
2. Read contributing guidelines:
https://github.com/go-gitea/gitea/blob/main/CONTRIBUTING.md
3. Describe what your pull request does and which issue you're targeting
(if any)

-->

This attempts to correct #21126 , where the content of the page is not
center-aligned.

(Note: I think this contains the right commits - but, those other
commits seem superfluous. I'm not sure I've made the pull request
correctly. I don't often use the pull request pattern when working,
opting to use the merge-request pattern instead for my workplace. If
there are any issues, please let me know and I will try to correct
them.)

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

templates/user/auth/webauthn.tmpl

@@ -1,7 +1,7 @@
 {{template "base/head" .}}
 <div class="user signin webauthn-prompt">
 	<div class="ui middle centered very relaxed page grid">
-		<div class="column">
+		<div class="column center aligned">
 				<h3 class="ui top attached header">
 				{{.locale.Tr "twofa"}}
 				</h3>