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

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What is the purpose of this pull request?

• [x] Bug fix
• [ ] New Feature
• [ ] Documentation update
• [ ] Other

Before submitting the PR, please make sure you do the following

• [x] Read the Contributing Guidelines, especially the Pull Request Guidelines.
• [x] Check that there isn't already a PR that solves the problem the same way to avoid creating a duplicate.
• [x] Provide a description in this PR that addresses what the PR is solving, or reference the issue that it solves (e.g. fixes #123).
• [x] Update the corresponding documentation if needed.
• [x] 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?