Prevent Stalebot from closing PRs (#5416)

Author: dplewis

.github/stale.yml

@@ -7,9 +7,14 @@ exemptLabels:
   - pinned
   - security
   - good first issue
-  - up for grabs
+  - up-for-grabs
+  - bug
+  - enhancement
+  - help wanted
 # Label to use when marking an issue as stale
 staleLabel: wontfix
+# Limit to only `issues` not `pulls`
+only: issues
 # Comment to post when marking an issue as stale. Set to `false` to disable
 markComment: >
   This issue has been automatically marked as stale because it has not had