ci: change "stale" limit to 20 days

Author: EndBug

.github/workflows/stale.yml

@@ -17,5 +17,5 @@ jobs:
           stale-pr-message: 'This PR is being marked as "stale" because it has been open 30 days with no activity. Remove the "stale" label or comment, otherwise this will be closed in 5 days.'
           stale-pr-label: stale
           exempt-pr-labels: pinned
-          days-before-stale: 30
+          days-before-stale: 20
           days-before-close: 5