[ci] Exclude flaky test headers from pytest summaries (#24365)
[ci] Exclude flaky test headers from pytest summaries (#24365)

Failing pytest summaries for flaky tests that eventually succeed are not always cleaned up properly: https://buildkite.com/ray-project/ray-builders-branch/builds/7292#_
This PR ensures we only print summaries when we have at least one summary file (and not just the header file).
ray-project/ray,ray-project/ray,ray-project/ray,ray-project/ray,ray-project/ray,ray-project/ray,ray-project/ray,ray-project/ray