chore(renovate): auto merge GitHub action PRs (#788)

Author: CFenner

.github/renovate.json

@@ -17,6 +17,13 @@
       ],
       "description": "Automerge check tools"
     },
+    {
+      "automerge": true,
+      "platformAutomerge": true,
+      "labels": ["maintenance"],
+      "matchManagers": ["github-actions"],
+      "description": "Automerge GitHub Actions"
+    },
     {
       "matchDatasources": ["pypi"],
       "groupName": "deprecated packages",