Fix javascript error when an anonymous user visiting migration page (#32144) (#32179)

backport #32144

This PR fixes javascript errors when an anonymous user visits the
migration page.
It also makes task view checking more restrictive.

The router moved from `/user/task/{id}/status` to
`/username/reponame/-/migrate/status` because it's a migrate status.

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

templates/repo/migrate/migrating.tmpl

@@ -7,7 +7,7 @@
 				{{template "base/alert" .}}
 				<div class="home">
 					<div class="ui stackable middle very relaxed page grid">
-						<div id="repo_migrating" class="sixteen wide center aligned centered column" data-migrating-task-id="{{.MigrateTask.ID}}">
+						<div id="repo_migrating" class="sixteen wide center aligned centered column" data-migrating-repo-link="{{.Link}}">
 							<div>
 								<img src="{{AssetUrlPrefix}}/img/loading.png">
 							</div>