bors.toml: use Buildkite status(es) instead of GitLab statuses?

Created by: DilumAluthge

Currently, the bors.toml file says this: https://github.com/JuliaGPU/KernelAbstractions.jl/blob/9d7a788054a03b882ea6d47e94ce390dd1247245/bors.toml#L1-L4

But, if I understand correctly, this repo now uses Buildkite for the GPU tests (not GitLab). Is that correct? If so, bors.toml line 2 (the line that says "ci/gitlab/%", ) should be changed to use the Buildkite status(es) instead of the GitLab statuses.