Use newly added exceptions to non default branch warning

Author: Urgau

triagebot.toml

@@ -984,12 +984,20 @@ cc = ["@Zalathar"]
 cc = ["@kobzol"]
 
 [assign]
-warn_non_default_branch = true
+warn_non_default_branch.enable = true
 contributing_url = "https://rustc-dev-guide.rust-lang.org/getting-started.html"
 users_on_vacation = [
     "jyn514",
 ]
 
+[[assign.warn_non_default_branch.exceptions]]
+title = "[beta"
+branch = "beta"
+
+[[assign.warn_non_default_branch.exceptions]]
+title = "[stable"
+branch = "stable"
+
 [assign.adhoc_groups]
 compiler = [
     "@BoxyUwU",