bk: avoid running LLVM on a schedule event (#635)

Author: v1v

.buildkite/pipeline.yml

@@ -82,9 +82,9 @@ steps:
                       - BUILDKITE_PULL_REQUEST_BASE_BRANCH=${BUILDKITE_PULL_REQUEST_BASE_BRANCH}
                       - GITHUB_PR_LABELS=${GITHUB_PR_LABELS}
 
-      # Trigger for the main branch only
+      # Trigger for the main branch only if no a scheduled build
       - label: ":pipeline: Upload llvm-apple Pipeline"
-        if: build.branch == 'main'
+        if: build.branch == 'main' && build.source != "schedule"
         command: "buildkite-agent pipeline upload .buildkite/llvm-apple-pipeline.yml"
         env:
           - BUILDKITE_PULL_REQUEST=${BUILDKITE_PULL_REQUEST}