The actual function we want for the format we're using is
decode_secret_key, not decode_openssh, apparently - covered this with a
toneest to make sure.
Change-Id: I659226169f213b8464b96aec6b94bf13fd80aac8
Reviewed-on: https://cl.tvl.fyi/c/depot/+/3863
Tested-by: BuildkiteCI
Reviewed-by: grfn <grfn@gws.fyi>