fix(legacy): emit css assets when cssCodeSplit and modernChuns is off

[armano2]

Description

This change allows assets to be emitted when renderModernChunks is set to false
i noticed this issue when i tried using cssCodeSplit: false with renderModernChunks: false

Additional context

Partially fixes issue #2062 #5901

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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 Contributing Guidelines, especially the Pull Request Guidelines.
• Check that there isn't already a PR that solves the problem the same way to avoid creating a duplicate.
• Provide a description in this PR that addresses what the PR is solving, or reference the issue that it solves (e.g. fixes #123).
• Update the corresponding documentation if needed.
• Ideally, include relevant tests that fail without this PR but pass with it.

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[armano2]

@patak-dev is there anything else that i have to do here?