Update dependency postcss-csso to v6 - autoclosed

This MR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
postcss-csso	5.0.1 -> 6.0.0

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Release Notes

lahmatiy/postcss-csso

v6.0.0

Compare Source

• Changed supported versions of Node.js to ^12.20.0, ^14.13.0 and >=15.0.0
• Converted to ES modules, CommonJS is supported as well (dual module)
• Bumped csso to 5.0

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Configuration

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