renovate: group github action updates (#274)

Author: andyasp

.github/renovate.json

@@ -18,6 +18,11 @@
              "matchDatasources": ["go"],
              "groupName": "go dependencies"
          },
+         {
+             "description": "Group all github action dependencies together to reduce noise",
+             "matchManagers": ["github-actions"],
+             "groupName": "github actions"
+         },
          {
              "description": "Disable Docker updates",
              "matchManagers": ["dockerfile"],