Update gh CLI steps in adding-a-new-ssh-key-to-your-github-account.md

[michelleN]

Why:

The GitHub CLI does not allow you to add an ssh key unless you are authenticated with your GitHub account. The gh auth login command not only authenticates you but also gives prompts to add your ssh key to your account. This PR amends the GitHub CLI portion with the gh auth login path. This may be useful to someone coming to this page for the first time who has not already installed the gh CLI and will do so as part of this flow and will then need to authenticate.

Closes #11721

What's being changed:

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Writer impact (This section is for GitHub staff members only):

• This pull request impacts the contribution experience
  • I have added the 'writer impact' label
  • I have added a description and/or a video demo of the changes below (e.g. a "before and after video")

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[github-actions]

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Content directory changes

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Source	Staging	Production	What Changed
content/authentication/connecting-to-github-with-ssh/adding-a-new-ssh-key-to-your-github-account.md	Modified	Original

[ramyaparimi]

@michelleN
Thanks so much for opening a PR! I'll get this triaged for review ⚡

[lecoursen]

Thanks @michelleN. Since the focus of this article is on adding an SSH key, let's mention the prerequisite of authenticating but link out for further details rather than including them here. I'll apply a suggestion to do that and then merge. 🎉

[github-actions]

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