fix: add actions:write permission to stale workflow (#2079)

The actions/stale@v10 action uses GitHub Actions cache to persist state
across runs. Without the actions:write permission, the action can write
cache entries but cannot delete them (403 error on cache cleanup).

This causes a vicious cycle: once an issue is processed and cached, the
action skips it on every future run with 'issue skipped due being
processed during the previous run' - so stale issues never reach the
closing logic after being marked stale.

Adding actions:write allows the action to properly manage its cache
lifecycle, enabling stale issues to be closed after the configured
30-day close window.

.github/workflows/stale.yml

@@ -6,6 +6,7 @@ on:
   workflow_dispatch: # Allow manual triggering
 
 permissions:
+  actions: write
   issues: write
   pull-requests: write