fix(linux-runner-image): install openssh-client for ssh-agent

What changed

Added openssh-client to the apt-get install layer in infra/linux-runner-image/Dockerfile, slotted next to git-lfs under the existing “VCS extras” category.

Why

Any workflow using webfactory/ssh-agent (or otherwise relying on ssh-agent, ssh-add, scp, or git-over-ssh) on the self-hosted Linux runner pool was failing at the SSH-setup step with:

The 'ssh-agent' executable could not be found.
##[error]spawnSync ssh-agent ENOENT

The Dockerfile was installing a fairly broad tooling layer but openssh-client was never on the list. GitHub’s hosted Ubuntu runner image ships it by default; this mirrors that posture so workflows portable from ubuntu-latest keep working on our pool.

Root cause

openssh-client (which provides ssh-agent) was simply absent from the package list. Confirmed via a failing job on tuist-tuist-runner-pool-linux-ubuntu-22-04-runner-… — ssh-agent was not on PATH and not installed anywhere on the image.

Impact

• Workflows using webfactory/ssh-agent on the Linux runner pool will succeed once the rebuilt image is digest-pinned into the managed-env values files (per infra/linux-runner-image/AGENTS.md).
• No behavior change for workflows that didn’t touch SSH.
• Marginal image-size increase (openssh-client is ~1 MB).

How to test locally

cd infra/linux-runner-image
docker build --pull -t tuist-linux-runner:ssh-test .
docker run --rm tuist-linux-runner:ssh-test ssh-agent -h

The last command should print ssh-agent usage (instead of “executable not found”).

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