fix: prevent production node_env in serve

[bluwy]

Description

Alternative to #9058
Fix #9057

Additional context

Make sure process.env.NODE_ENV is not production in dev. Some plugins may rely on this behaviour for hmr / improved perf for example, so we can't have production-like behaviours in dev.

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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• Read the Pull Request Guidelines and follow the Commit Convention.
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[patak-dev]

Merging as @bluwy tested with vite-ecosystem-ci that this fix works for everyone.