fix(deps): update dependency @netlify/build to ^28.1.15

[renovate]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
@netlify/build	^28.1.13 -> ^28.1.15

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[github-actions]

📊 Benchmark results

Comparing with a2913ba

Package size: 248 MB

⬆️ 0.17% increase vs. a2913ba

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• T (current commit): 248 MB