Pin workflow.

Author: chungyc

.github/workflows/stale.yml

@@ -19,7 +19,7 @@ jobs:
       pull-requests: write
 
     steps:
-    - uses: actions/stale@v5
+    - uses: actions/stale@f7176fd3007623b69d27091f9b9d4ab7995f0a06 # v5.2.1
       with:
         days-before-stale: 90
         days-before-close: 30