fix(ci): Add python-dateutil dependency to stale-bot workflow

The stale-bot workflow failed with ModuleNotFoundError because adk_stale_agent imports python-dateutil but the runner environment did not have it installed. Added python-dateutil to the pip install step.

Change-Id: I1002c8eb7bb8fe2f9e106e85c3b5a7f990fe1c62

Author: xuanyang15

.github/workflows/stale-bot.yml

@@ -29,7 +29,7 @@ jobs:
       - name: Install dependencies
         run: |
           python -m pip install --upgrade pip
-          pip install requests google-adk
+          pip install requests google-adk python-dateutil
 
       - name: Run Auditor Agent Script
         env: