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>

routers/api/v1/api.go

@@ -202,7 +202,7 @@ func repoAssignment() func(ctx *context.APIContext) {
 			if needTwoFactor {
 				ctx.Repo.Permission = access_model.PermissionNoAccess()
 			} else {
-				ctx.Repo.Permission, err = access_model.GetUserRepoPermission(ctx, repo, ctx.Doer)
+				ctx.Repo.Permission, err = access_model.GetDoerRepoPermission(ctx, repo, ctx.Doer)
 				if err != nil {
 					ctx.APIErrorInternal(err)
 					return