ci: Add exempt-pr-label to stale action (#281)

Author: abmusse

.github/workflows/stale.yml

@@ -17,6 +17,7 @@ jobs:
         stale-pr-message: ':wave: Hi! This pull request has been marked stale due to inactivity. If no further activity occurs, it will automatically be closed.'
         stale-issue-label: 'stale'
         exempt-issue-label: 'keep-open'
+        exempt-pr-label: 'keep-open'
         stale-pr-label: 'stale'
         days-before-stale: 30
         days-before-close: 7