docs: improve code block syntax highlighting by changing js → javascript

[premtimb]

Description

This PR updates the code block language identifier from js to javascript in the Arrays documentation.
Using javascript provides improved syntax highlighting and maintains consistency with other Codecademy Docs pages.

Motivation

This change improves readability for learners and keeps the formatting consistent across the documentation.

Files Changed

• content/javascript/concepts/arrays/arrays.md

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[mamtawardhani]

Closing this PR as the original content is correct