chore(deps): group stylelint dependencies in renovate config

renovate.json

@@ -12,6 +12,13 @@
         "registry.gitlab.com/unboundsoftware/schemas-app"
       ],
       "enabled": false
+    },
+    {
+      "groupName": "stylelint",
+      "matchPackageNames": [
+        "stylelint",
+        "stylelint-config-standard"
+      ]
     }
   ]
 }