fix(testing): use happy-dom for preloader isBrowser check

[maiieul]

What is it?

• Bug

Description

Checklist

• My code follows the developer guidelines of this project
• I performed a self-review of my own code
• I added a changeset with pnpm change
• I made corresponding changes to the Qwik docs
• I added new tests to cover the fix / functionality

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🦋 Changeset detected

Latest commit: 4f40f33

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commit: 4f40f33

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