add back explicit termination of preauth child process

[tgauth]

PR Summary

• add back code that was removed starting in V8.9 which prevented the pre-auth child process from being terminated when LoginGraceTime expired, potentially leading to a build-up of orphaned child processes until the corresponding client disconnected
• update LoginGraceTime pester test

PR Context

• sshd-session.exe and LoginGraceTIme Win32-OpenSSH#2409
• V8.6: https://github.com/PowerShell/openssh-portable/blob/v8.6.0.0/sshd.c#L366-L385
• V8.9: https://github.com/PowerShell/openssh-portable/blob/v8.9.0.0/sshd.c#L382-L397
• related upstream commit: openssh@4e62c13

[Copilot]

Pull Request Overview

This PR fixes the grace alarm handler behavior on Windows to ensure both session processes exit when LoginGraceTime expires, and includes a minor formatting correction.

• Added Windows-specific logic to explicitly kill the child process when the login grace period expires
• Updated test expectations to verify both session processes exit after grace timeout
• Removed trailing whitespace from a comment

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
sshd-session.c	Added Windows-specific grace alarm handler to kill child process via pmonitor PID; removed trailing whitespace from comment
regress/pesterTests/SSHD.Tests.ps1	Updated test assertion to expect both session processes to exit after LoginGraceTime expires

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[tgauth]

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[vthiebaut10]

Is this trailing space from upstream? I would leave it unchanged if that is the case just to reduce discrepancies