chore: update current minor release branch in mergify.yml (#8960)

Co-authored-by: anmolshres98 <anmolshres98@users.noreply.github.com>

Author: anmolshres98

.github/mergify.yml

@@ -39,6 +39,6 @@ pull_request_rules:
       backport:
         branches:
           # current minor release branch
-          - "release/5.2.x"
+          - "release/5.6.x"
           # previous major release branch
           - "release/4.11.x"