fix: fix default import.meta.env.PROD: false

[hi-ogawa]

Description

• a part of [🐞BUG]: import.meta.env.PROD has the wrong value, even if stubbed. #5525

setupEnv added in #5476 was assigning boolean values from config.env to process.env (such as config.env.PROD: false). I fixed it by copying the same PROD/DEV specific logic from VitestPlugin.configResolved:

vitest/packages/vitest/src/node/plugins/index.ts

Lines 162 to 172 in 643bed6

	// we replace every "import.meta.env" with "process.env"
	// to allow reassigning, so we need to put all envs on process.env
	const { PROD, DEV, ...envs } = viteConfig.env
	// process.env can have only string values and will cast string on it if we pass other type,
	// so we are making them truthy
	process.env.PROD ??= PROD ? '1' : ''
	process.env.DEV ??= DEV ? '1' : ''
	for (const name in envs)
	process.env[name] ??= envs[name]

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