docs: Add PowerShell v6+ prerequisite for Windows users to Copilot CLI install guide

[aymanaboghonim]

Copilot Chat generated this pull request.

Prompt summary - submitted by @aymanaboghonim

Add a Windows-specific prerequisite for PowerShell v6+ to the Copilot CLI install guide, as required by the official documentation. No other changes were made.

Summary:
This PR surgically adds a single prerequisite line for Windows users to the Copilot CLI installation guide, ensuring the documentation matches the official requirements. No other content was changed.

Reference:
See the official Copilot CLI prerequisites: https://github.com/github/copilot-cli?tab=readme-ov-file#prerequisites

[Copilot]

Pull Request Overview

This PR adds a Windows-specific prerequisite for PowerShell version 6 or later to the Copilot CLI installation guide, aligning the documentation with the official requirements.

• Added PowerShell v6+ prerequisite for Windows users in the prerequisites list

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[github-actions]

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Source	Review	Production	What Changed
copilot/how-tos/set-up/install-copilot-cli.md	fpt ghec	fpt ghec

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[Sharra-writes]

@aymanaboghonim Our documentation for Windows is often lacking, so I'll definitely look into this.

[github-actions]

A stale label has been added to this pull request because it has been open 30 days with no activity. If you think this pull request should remain open, please add a new comment.

[github-actions]

A stale label has been added to this pull request because it has been open 30 days with no activity. If you think this pull request should remain open, please add a new comment.

[aymanaboghonim]

Hi @Sharra-writes! 👋

I was checking the conflicts today and noticed that the main branch has already been updated to include the PowerShell v6+ prerequisite. Since the documentation is now accurate and aligns with the requirements, this PR is effectively redundant.

I’ll close this out myself to keep your backlog clean and tidy. Thanks for the initial review and for looking into the Windows docs!

Happy New Year to you and the team! 🎆