Update allowed-labels.yml (#4524)

* Update allowed-labels.yml

Adds label for cross-service team PRs. To be ignored by the on-call flow and managed/shepherded by the Cross Service team.

* Updates the Label Checker as well to only check the main branch

---------

Co-authored-by: Jason Q <[email protected]>

Author: DavidSouther

.github/allowed-labels.yml

@@ -129,4 +129,7 @@
   description: "A medium amount of effort/complexity"
 - name: size/large
   color: "adb5bd"
-  description: "A large amount of effort/complexity"
+  description: "A large amount of effort/complexity"
+- name: cross-service-team
+  color: "e0cdff"
+  description: "PRs for the Cross Service Cloud Sherpas"

.github/workflows/label-checker.yml

@@ -2,6 +2,8 @@
 name: Label Checker
 on:
   pull_request:
+    branches:
+      - main
     types:
       - opened
       - synchronize