* [Buildkite] Enable automatic retries for failed github artifact step
This is to handle failures which may occur when attempting to upload assets, per: https://buildkite.com/authelia/authelia/builds/465#537f931f-efc3-4f7b-9527-c927c1425a52.
* [Buildkite] Ensure GitHub artifact step is reported as a failure
When the initial command fails and we remove the release, we need to ensure that the exit status is reported as non-zero to trigger the automatic retry.
