disable fleet-server-tests on prs (#2754)

Author: juliaElastic

catalog-info.yaml

@@ -129,6 +129,9 @@ spec:
     spec:
       repository: elastic/fleet-server
       pipeline_file: .buildkite/pipeline.service-tests.yml
+      branch_configuration: "main"
+      provider_settings:
+        build_pull_requests: false
       teams:
         cloud-k8s-region:
           access_level: MANAGE_BUILD_AND_READ