Update CSS preprocessors

[renovate]

This PR contains the following updates:

Package	Change	Age	Confidence
autoprefixer	10.5.2 → 10.5.4
postcss (source)	8.5.16 → 8.5.21

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Release Notes

postcss/autoprefixer (autoprefixer)

v10.5.4

Compare Source

• Fixed prefixed rule duplication (by @​xianjianlf2).

v10.5.3

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• Fixed brackets and gradient parser (@​alanturing881).

postcss/postcss (postcss)

v8.5.21

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• Fixed childless at-rule losing semicolon before comment (by @​sarathfrancis90).
• Fixed docs (by @​isker).

v8.5.20

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• Fixed missing space if AtRule#params is set after (by @​sarathfrancis90).
• Fixed mixing AST error on warnings (by @​MahinAnowar).

v8.5.19

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• Fixed cleaning before for new nodes inserted to Root (by @​MahinAnowar).

v8.5.18

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• Restricted loading previous source maps file to the opts.from folder for security reasons (use unsafeMap: true to disable the check).

v8.5.17

Compare Source

• Fixed Maximum call stack size exceeded error.
• Fixed Prototype hijacking for postcss.fromJSON().
• Fixed Input#origin() for unmapped end position (by @​chatman-media).

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