Tiny markdown fix for "articles" in git-github-fundamentals.md

[PeterSmithRedmond]

Tiny markdown fix: in one place the word articles had was surrounded by an inconsistent number of back-ticks (1 before and 2 afterwards).

Fixed by surrounding it by 1 back-tick to match what was done earlier in the same sentence. Verified by looking at the 'preview' Windows

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[learn-build-service-prod]

Learn Build status updates of commit 4e3afb8:

✅ Validation status: passed

File	Status	Preview URL	Details
Contribute/content/git-github-fundamentals.md	✅Succeeded	View

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