chore(deps): lock python version 3.9 in renovate

renovate.json

@@ -5,5 +5,13 @@
   "dependencyDashboard": true,
   "timezone": "Asia/Shanghai",
   "schedule": "after 4am and before 8am every saturday",
-  "labels": ["dependencies", "bot"]
+  "labels": ["dependencies", "bot"],
+  "packageRules": [
+    {
+      "matchPackageNames": [
+        "python"
+      ],
+      "allowedVersions": "3.9"
+    }
+  ]
 }