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/activity.go

@@ -15,9 +15,9 @@ import (
 )
 
 func ToActivity(ctx context.Context, ac *activities_model.Action, doer *user_model.User) *api.Activity {
-	p, err := access_model.GetUserRepoPermission(ctx, ac.Repo, doer)
+	p, err := access_model.GetDoerRepoPermission(ctx, ac.Repo, doer)
 	if err != nil {
-		log.Error("GetUserRepoPermission[%d]: %v", ac.RepoID, err)
+		log.Error("GetDoerRepoPermission[%d]: %v", ac.RepoID, err)
 		p.AccessMode = perm_model.AccessModeNone
 	}