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>

tests/integration/api_pull_review_test.go

@@ -498,7 +498,7 @@ func TestAPIPullReviewStayDismissed(t *testing.T) {
 		pullIssue.ID, user8.ID, 1, 1, 2, false)
 
 	// user8 dismiss review
-	permUser8, err := access_model.GetUserRepoPermission(t.Context(), pullIssue.Repo, user8)
+	permUser8, err := access_model.GetIndividualUserRepoPermission(t.Context(), pullIssue.Repo, user8)
 	assert.NoError(t, err)
 	_, err = issue_service.ReviewRequest(t.Context(), pullIssue, user8, &permUser8, user8, false)
 	assert.NoError(t, err)