fix(ssh): fix windows openssh agent detection logic (#10954)

On Windows, checking for the existence of the OpenSSH agent named pipe
(`\\.\pipe\openssh-ssh-agent`) can throw an `EBUSY` error if the agent
is running and the pipe is in use. Previously, this error was caught
generically and treated as the pipe not existing, causing auto-detection
to fail even when the agent was active.

This change updates the detection logic to explicitly catch `EBUSY`
errors from `fs.stat` and treat them as a positive signal that the
pipe exists.