fix: make <build> route exclusion rule only exclude static assets

[Begad666]

Fixes #13385

The original rule of /_app/* broke apps with pre-rendered pages and pages using dynamic environment variables simultaneously, because it excludes /_app/env.js, which is loaded in pre-rendered pages. This fixes it by only excluding the assets generated by Vite.

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[eltigerchino]

Thank you!