Is it possible to override the ssh command? (GIT_SSH_COMMAND)

[larsnystrom]

I need to proxy the ssh connection due to an outgoing corporate firewall. Therefore, I need to override the SSH command. I've tried to update the PATH with a script, but actions/checkout@v4 doesn't seem to use it (even though it looks like it should, as it's calling out to which to find the ssh bin).

Is there some other way I can do this?

If not, how can do the equivalent of

uses: actions/checkout@v4
with:
  ssh-key: ${{ secrets.PRIVATE_SSH_KEY }}

using regular git?