Scripts: Fix code comment about extra scripts sourceURL

[sirreal]

@TobiasBg noticed a typo in a code comment from [60719].

Trac ticket: https://core.trac.wordpress.org/ticket/63887

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Pull Request Overview

This PR fixes a grammatical error in a code comment that explains why sourceURL comments are not printed when script concatenation is enabled.

• Corrects "may a concatenated script" to "may break concatenated scripts"
• Improves clarity by changing "multiple are joined" to "multiple scripts are joined"

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[sirreal]

Merged in [60722].