Fix issue label deletion with Actions tokens (#37013)

Use shared repo permission resolution for Actions task users in issue
label remove and clear paths, and add a regression test for deleting
issue labels with a Gitea Actions token.

This fixes issue label deletion when the request is authenticated with a
Gitea Actions token.
Fixes #37011 

The bug was that the delete path re-resolved repository permissions
using the normal user permission helper, which does not handle Actions
task users. As a result, `DELETE
/api/v1/repos/{owner}/{repo}/issues/{index}/labels/{id}` could return
`500` for Actions tokens even though label listing and label addition
worked.

---------

Co-authored-by: Codex <codex@openai.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: Giteabot <teabot@gitea.io>

services/convert/notification.go

@@ -25,9 +25,9 @@ func ToNotificationThread(ctx context.Context, n *activities_model.Notification)
 
 	// since user only get notifications when he has access to use minimal access mode
 	if n.Repository != nil {
-		perm, err := access_model.GetUserRepoPermission(ctx, n.Repository, n.User)
+		perm, err := access_model.GetIndividualUserRepoPermission(ctx, n.Repository, n.User)
 		if err != nil {
-			log.Error("GetUserRepoPermission failed: %v", err)
+			log.Error("GetIndividualUserRepoPermission failed: %v", err)
 			return result
 		}
 		if perm.HasAnyUnitAccessOrPublicAccess() { // if user has been revoked access to repo, do not show repo info