Fix Arch repo pacman.conf snippet (#35825)

Current template uses the owner followed by the instance URL as the repo
name. Technically this can work if the repo happens to be named the
exact same way. But if, for example, you follow [the
docs](https://docs.gitea.com/usage/packages/arch/#publish-a-package),
you'll end up with a package in `core` while the pacman conf refers to a
non-existent repo `testuser.gitea.example.com`. Whatever is in the
square brackets get substituted in for `$repo`, so we do not want
anything except the exact repo name there.

And since it's now referring to the repo and not the owner, I've updated
the pacman conf to show all repositories.

---------

Co-authored-by: Giteabot <teabot@gitea.io>

templates/package/content/arch.tmpl

@@ -4,9 +4,11 @@
 		<div class="ui form">
 			<div class="field">
 				<label>{{svg "octicon-gear"}} {{ctx.Locale.Tr "packages.arch.registry"}}</label>
-				<div class="markup"><pre class="code-block"><code>[{{.PackageDescriptor.Owner.LowerName}}.{{.PackageRegistryHost}}]
+				<div class="markup"><pre class="code-block"><code>{{range $i, $repo := .Repositories}}{{if $i}}
+{{end}}[{{$repo}}]
 SigLevel = Optional TrustAll
-Server = <origin-url data-url="{{AppSubUrl}}/api/packages/{{.PackageDescriptor.Owner.Name}}/arch/$repo/$arch"></origin-url></code></pre></div>
+Server = <origin-url data-url="{{AppSubUrl}}/api/packages/{{$.PackageDescriptor.Owner.Name}}/arch/$repo/$arch"></origin-url>
+{{end}}</code></pre></div>
 			</div>
 			<div class="field">
 				<label>{{svg "octicon-sync"}} {{ctx.Locale.Tr "packages.arch.install"}}</label>