Exempt pull requests from stalebot

.github/stale.yml

@@ -1,5 +1,8 @@
 # Configuration for Stale (https://github.com/apps/stale)
 
+# Pull requests are exempt from being marked as stale
+only: issues
+
 # Number of days of inactivity before an issue becomes stale
 daysUntilStale: 14