test: add sugarss sourcemap test

[sapphi-red]

Description

This PR removes duplicated test in playground/css-sourcemap/__tests__/css-sourcemap.spec.ts and adds test for sugarss's sourcemap.

refs #6705

Additional context

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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

• Read the Contributing Guidelines.
• Read the Pull Request Guidelines and follow the Commit Convention.
• 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).
• Ideally, include relevant tests that fail without this PR but pass with it.