chore(ci): make merge-conditions job copy/pastable

Refs: forgejo/forgejo#5999

.forgejo/workflows/merge-requirements.yml

@@ -1,7 +1,7 @@
 # Copyright 2024 The Forgejo Authors
 # SPDX-License-Identifier: MIT
 
-name: requirements
+name: issue-labels
 
 on:
   pull_request:
@@ -9,19 +9,26 @@ on:
       - labeled
       - edited
       - opened
-      - synchronize
 
 jobs:
   merge-conditions:
-    if: vars.ROLE == 'forgejo-coding'
+    if: >
+      vars.ROLE == 'forgejo-coding' &&
+
+      github.event_name == 'pull_request' &&
+      (
+        github.event.action == 'label_updated' ||
+        github.event.action == 'edited' ||
+        github.event.action == 'opened'
+      )
     runs-on: docker
     container:
       image: 'code.forgejo.org/oci/node:20-bookworm'
     steps:
-      - name: Debug output
+      - name: Debug info
         run: |
           cat <<'EOF'
-          ${{ toJSON(github.event) }}
+          ${{ toJSON(github) }}
           EOF
       - name: Missing test label
         if: >