feat: accept AcceptedPlugin type for postcss plugin

[sapphi-red]

Description

Changed { plugins?: postcss.Plugin[] } into { plugins?: postcss.AcceptedPlugin[] }.
Because postcss accepts AcceptedPlugin[].
https://github.com/postcss/postcss/blob/a4f6733ae0660c3631611e754b4df6a42b508d1d/lib/postcss.d.ts#L348-L364

close #8826

Additional context

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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