T7878: Using mergify rule to handle conflict checks for private repo

.github/mergify.yml

@@ -0,0 +1,10 @@
+pull_request_rules:
+  - name: Label conflicting pull requests
+    description: Add a label to a pull request with conflict to spot it easily
+    conditions:
+      - conflict
+      - '-closed'
+    actions:
+      label:
+        toggle:
+          - conflict

.github/workflows/check-pr-conflicts.yml

@@ -9,6 +9,7 @@ permissions:
   contents: read
 
 jobs:
-  check-pr-conflict-call:
+  check-pr-conflict:
+    if: github.repository_owner == 'vyos'
     uses: vyos/.github/.github/workflows/check-pr-merge-conflict.yml@current
     secrets: inherit