chore: group Go version and golang Docker image updates in Renovate

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: koki-develop

renovate.json

@@ -15,6 +15,11 @@
     }
   ],
   "packageRules": [
+    {
+      "groupName": "Go",
+      "matchDatasources": ["golang-version", "docker"],
+      "matchDepNames": ["go", "golang"]
+    },
     {
       "matchFileNames": ["Dockerfile"],
       "semanticCommitType": "fix"