Update about-authentication-to-github.md

[akoper]

Improve grammar and readability: sentence has parallel structure and removes duplicative articles.

Why:

Closes:

What's being changed (if available, include any code snippets, screenshots, or gifs):

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• A subject matter expert (SME) has reviewed the technical accuracy of the content in this PR. In most cases, the author can be the SME. Open source contributions may require a SME review from GitHub staff.
• The changes in this PR meet the docs fundamentals that are required for all content.
• All CI checks are passing.

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Content directory changes

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Source	Preview	Production	What Changed
authentication/keeping-your-account-and-data-secure/about-authentication-to-github.md	fpt ghec ghes@ 3.15 3.14 3.13 3.12 3.11 3.10	fpt ghec ghes@ 3.15 3.14 3.13 3.12 3.11 3.10

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fpt: Free, Pro, Team
ghec: GitHub Enterprise Cloud
ghes: GitHub Enterprise Server

Mistake

[nguyenalex836]

@akoper Thank you for raising this PR and your willingness to contribute! ✨ However, as these changes are mainly personal preferences on how to phrase something rather than corrections or improvements, I'm afraid we aren't able to accept this contribution 🙇

If you'd like to make changes I'd recommend raising an improvement issue here, then someone from the team can take a look at your proposal before you go ahead.

For more information about contributing, and our house style, see https://docs.github.com/en/contributing 💛