Update dependency postcss to v8.4.12

This MR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
postcss (source)	8.4.5 -> 8.4.12

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Release Notes

postcss/postcss

v8.4.12

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• Fixed package.funding to have same value between all PostCSS packages.

v8.4.11

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• Fixed Declaration#raws.value type.

v8.4.10

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• Fixed package.funding URL format.

v8.4.9

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• Fixed package.funding (by Álvaro Mondéjar).

v8.4.8

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• Fixed end position in empty Custom Properties.

v8.4.7

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• Fixed Node#warn() type (by Masafumi Koba).
• Fixed comment removal in values after ,.

v8.4.6

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• Prevented comment removing when it change meaning of CSS.
• Fixed parsing space in last semicolon-less CSS Custom Properties.
• Fixed comment cleaning in CSS Custom Properties with space.
• Fixed throwing an error on .root access for plugin-less case.

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