"Try Update Last Green Commit" regularly fails, but succeeds when retried

[mostynb]

I noticed that the tip of the master branch in the bazel-remote repository often has a red cross because the "Try Update Last Green Commit" job has failed with error message Cannot update last green commit due to 1 failing step(s): :cop: Validate .bazelci/presubmit.yml, despite everything else being green. And when I retry the build, it turns green.

For example: https://buildkite.com/bazel/bazel-remote-cache/builds/1587#d6a00835-c7a9-4a07-a2b7-b7af22ff45eb

I can't tell if there's a problem with my yaml file (all the steps run and pass), or if this is a bazelci bug.