Bump the npm group in /src/sphinx_antsibull_ext/css with 2 updates

[dependabot]

Bumps the npm group in /src/sphinx_antsibull_ext/css with 2 updates: cssnano and postcss.

Updates cssnano from 7.1.2 to 7.1.3

Release notes

Sourced from cssnano's releases.

v7.1.3

What's Changed

• Optimize mergeRule selector merging with WeakMap caching by @​Goodwine in cssnano/cssnano#1748

Full Changelog: https://github.com/cssnano/cssnano/compare/cssnano@7.1.2...cssnano@7.1.3

Commits

• b2e9903 Publish cssnano 7.1.3
• a9f72ef chore: update development dependencies
• 5674f7a fix(postcss-svgo: update SVGO
• c3e537a fix: update postcss-selector-parser
• 5b9af42 fix: update browserlist and autoprefixer
• c0053c8 chore: add changeset
• da88eca Optimize selector merging with WeakMap caching
• cf4fc27 chore(deps-dev): bump diff from 8.0.2 to 8.0.3
• a985c71 chore: update pnpm
• 4b2a74a chore: update to ESLint 10
• Additional commits viewable in compare view

Updates postcss from 8.5.6 to 8.5.8

Release notes

Sourced from postcss's releases.

8.5.8

• Fixed Processor#version.

8.5.7

• Improved source map annotation cleaning performance (by CodeAnt AI).

Changelog

Sourced from postcss's changelog.

8.5.8

• Fixed Processor#version.

8.5.7

• Improved source map annotation cleaning performance (by CodeAnt AI).

Commits

• 65de537 Release 8.5.8 version
• b2c6d97 Run git hook register
• 0ae0a49 Update Processor#version
• 6ee9f14 Release 8.5.7 version
• 3fbc951 Fix uvu Node.js 25 support
• 52db53e Update dependencies
• 497daef Speed up source map annotation cleaning by moving from RegExp
• 41e739a Remove banner
• 1329142 chore: speed up space-only string check in lib/parser.js (#2064)
• 23beff9 Update dependencies
• Additional commits viewable in compare view

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