Renovate: disable anything else except pub & github actions

Author: jpnurmi

renovate.json

@@ -2,5 +2,9 @@
   "$schema": "https://docs.renovatebot.com/renovate-schema.json",
   "extends": [
     "config:base"
+  ],
+  "enabledManagers": [
+    "github-actions",
+    "pub"
   ]
 }