Update stale.yml

Only use with issues and not pull requests for now

Author: wahln

.github/stale.yml

@@ -21,3 +21,6 @@ closeComment: >
   activity in four weeks. This happens usually when the issue has already
   been solved or it is no longer relevant. If that's not the case,
   feel free to reopen the issue.
+
+#Only use on issues for now
+only: issues