chore: update dependency cssnano to v6

[renovate]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
cssnano	^5.1.13 -> ^6.0.0

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Release Notes

cssnano/cssnano (cssnano)

v6.0.3: v6.0.3

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Bug fixes

• do not sort unknown properties\

Other

• Require latest browserslist and postcss-selector-parser

v6.0.2: v6.0.2

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• fix: update cssnano peer dependency to 8.4.31 to avoid security issue
• fix: update postcss-calc to 9.0.1 to solve disappearing expressions inside two brackets
• deps(postcss-svgo): update SVGO to 3.0.5 and update doc
• chore: update css-declaration-sorter
• fix(postcss-minify-selectors): prevent mangling of timeline range names
• fix(postcss-convert-values): keep percent unit in @Property
• chore(cssnano): update lilconfig to 3.0.0

v6.0.1: v6.0.1

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Bug Fixes

• fix(postcss-merge-rules): do not merge nested rules (cssnano/cssnano@eb9a9a1)
• fix(postcss-reduce-idents): minify grid line names correctly (cssnano/cssnano@2af6687)

v6.0.0: v6.0.0

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Major Changes

• 99d1e6a: postcss-normalize-url: remove normalize-url configuration options
• 4e272f8: postcss-svgo: Upgrade dependency svgo to v3 and increase the minimum supported node version to v14
• ca9d3f5: Switch minimum supported Node version to 14 for all packages
• 39a2040: feat!(cssnano): remove undocumented YAML config support

Migration instructions

• If you're not happy with the defaults for the normalize-url transform, turn it off completely. Options were removed as most would change the meaning of the URL, which is unexpcted in the case of CSS minification.
• In the unlikely event you're using YAML to configure cssnano, move the cssnano configuration inside the PostCSS config or use a configuration file in CommonJS or JSON format.

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Configuration

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