Update stale.yml

A change in permissions policy for GitHub actions within Microsoft's GitHub Enterprise requires that this permission block be added to the Stalebot config file.

Author: huypub

.github/workflows/stale.yml

@@ -1,5 +1,9 @@
 name: Mark stale pull requests
 
+permissions:
+  issues: write
+  pull-requests: write
+  
 on:
   schedule:
   - cron: "0 */6 * * *"