chore: let frappe pr bot raise stable branch PRs

[skip ci]
diff --git a/.mergify.yml b/.mergify.yml
index d7f82e6..c5f3d83 100644
--- a/.mergify.yml
+++ b/.mergify.yml
@@ -9,6 +9,7 @@
           - author!=nabinhait
           - author!=ankush
           - author!=deepeshgarg007
+          - author!=frappe-pr-bot
           - author!=mergify[bot]
 
         - or: