[Close stale PRs] Skip RFCs and "Waiting on Review"

Pull requests with the "Waiting on Author" label should still not be
closed if they have the RFC label as closing them requires manual
action. Also avoid closing "Waiting on Review".

Author: iluuu1994

.github/workflows/close-stale-prs.yml

@@ -12,6 +12,7 @@ jobs:
         with:
           days-before-close: 7
           days-before-stale: 60
+          exempt-pr-labels: RFC,Waiting on Review
           # Temporary, avoid closing PRs until this action merged
           debug-only: true
           # Hack to skip issues, unfortunately there's no option to disable issues