chore: group GitHub-maintained actions (actions/*, github/*) in renovate

Reduces Renovate PR noise by grouping updates to GitHub Actions that are
maintained by GitHub/Microsoft. Third-party actions stay ungrouped so
their update cadence and review context remain independent.

Author: vlsi

renovate.json

@@ -61,6 +61,17 @@
         "com.helger{/,}**"
       ]
     },
+    {
+      "groupName": "github official actions",
+      "description": "actions/* and github/* are maintained by GitHub/Microsoft and can be updated together",
+      "matchManagers": [
+        "github-actions"
+      ],
+      "matchPackageNames": [
+        "actions/**",
+        "github/**"
+      ]
+    },
     {
       "groupName": "io.burt",
       "matchPackageNames": [