This is in preparation for a subsequent CL that will do much more
significant changes in //nix/buildkite.
Change-Id: I80a8d67d3a7d593854c8d711572483c2581e7881
Reviewed-on: https://cl.tvl.fyi/c/depot/+/5824
Reviewed-by: ezemtsov <eugene.zemtsov@gmail.com>
Tested-by: BuildkiteCI