Bump is-svg and postcss-svgo in /src/frontend

[dependabot[bot]]

Removes is-svg. It's no longer used after updating ancestor dependency postcss-svgo. These dependencies need to be updated together.

Removes is-svg

Updates postcss-svgo from 4.0.1 to 4.0.3

Release notes

Sourced from postcss-svgo's releases.

4.0.3

Bug Fixes

• postcss-merge-longhand incorrect minification of border (border-*) declarations.

4.0.2

Bug Fixes

• postcss-merge-longhand don't explode declarations with custom properties.
• postcss-colormin now better transform to hsl.

Commits

• dd457b2 chore(release): 4.0.3
• 9a70605 fix(postcss-merge-longhand): not mangle border output (#555)
• c4f2e59 fix: incorrect merging of border declarations (#551) (#552)
• ed5c54e Remove v4 notice on homepage
• e7740da chore(release): 4.0.2
• d28796c fix(postcss-merge-longhand): don't explode declarations with custom propertie...
• 1c3cb43 fix(postcss-colormin): bug where color value is mutated (#546)
• 9b6686b docs(site): update (#544)
• a8bd5d5 docs: remove css-loader from docs (#543)
• 0fe325d docs: update CHANGELOG
• See full diff in compare view

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