chore(ci): make backporting job copy/pastable

Refs: forgejo/forgejo#5999

.forgejo/workflows/backport.yml

@@ -1,27 +1,8 @@
 # Copyright 2024 The Forgejo Authors
 # SPDX-License-Identifier: MIT
 #
-# To modify this workflow:
-#
-#  - change pull_request_target: to  pull_request:
-#    so that it runs from a pull request instead of the default branch
-#
-#  - push it to the wip-ci-backport branch on the forgejo repository
-#    otherwise it will not have access to the secrets required to push
-#    the PR
-#
-#  - open a pull request targetting wip-ci-backport that includes a change
-#    that can be backported without conflict in v1.21 and set the
-#    `backport/v1.21` label.
-#
-#  - once it works, open a pull request for the sake of keeping track
-#    of the change even if the PR won't run it because it will use
-#    whatever is in the default branch instead
-#
-#  - after it is merged, double check it works by setting a
-#    `backport/v1.21` label on a merged pull request that can be backported
-#    without conflict.
-#
+name: issue-labels
+
 on:
   pull_request_target:
     types:
@@ -31,16 +12,20 @@ on:
 jobs:
   backporting:
     if: >
-      ( vars.ROLE == 'forgejo-coding' ) && (
-        github.event.pull_request.merged
-        &&
+      vars.ROLE == 'forgejo-coding' &&
+
+      secrets.BACKPORT_TOKEN != '' &&
+
+      github.event_name == 'pull_request_target' &&
+      (
+        github.event.pull_request.merged &&
         contains(toJSON(github.event.pull_request.labels), 'backport/v')
       )
     runs-on: docker
     container:
       image: 'code.forgejo.org/oci/node:20-bookworm'
     steps:
-      - name: event info
+      - name: Debug info
         run: |
           cat <<'EOF'
           ${{ toJSON(github) }}