This release includes the contribution by @thommyhh from #27.
Unless the SSH_AUTH_SOCK is configured explicitly, the SSH agent will now use a random file name for the socket. That way, multiple, concurrent SSH agents can be used on non-ephemeral, self-hosted runners.
A new post-action step will automatically clean up the running agent at the end of a job.
Be aware of the possible security implications: Two jobs running on the same runner might be able to access each other's socket and thus access repositories and/or hosts.