ci: chore adjust renovate to combine go toolchain and go docker updates (#47)

Reviewed-on: #47
Co-authored-by: t.behrendt <t.behrendt@t00n.de>
Co-committed-by: t.behrendt <t.behrendt@t00n.de>

renovate.json

@@ -1,3 +1,12 @@
 {
-  "$schema": "https://docs.renovatebot.com/renovate-schema.json"
+  "$schema": "https://docs.renovatebot.com/renovate-schema.json",
-}
+  "packageRules": [
+    {
+      "matchPackageNames": [
+        "golang",
+        "go"
+      ],
+      "groupName": "go version"
+    }
+  ]
+}