Update mergify rules (#1353)

.mergify.yml

@@ -1,7 +1,7 @@
 queue_rules:
   - name: default
     conditions:
-      - check-success=elastic-package/pr-merge
+      - check-success=buildkite/elastic-package
 
 pull_request_rules:
   - name: automatic approval for Dependabot pull requests
@@ -13,7 +13,7 @@ pull_request_rules:
         message: Automatically approving dependabot
   - name: automatic merge of bot 🤖
     conditions:
-      - check-success=elastic-package/pr-merge
+      - check-success=buildkite/elastic-package
       - check-success=CLA
       - base=main
       - author~=^dependabot(|-preview)\[bot\]$