Bump d3-color and @decidim/core

Bumps [d3-color](https://github.com/d3/d3-color) to 3.1.0 and updates ancestor dependency [@decidim/core](https://github.com/decidim/decidim/tree/HEAD/packages/core). These dependencies need to be updated together.


Updates `d3-color` from 1.4.1 to 3.1.0
- [Release notes](https://github.com/d3/d3-color/releases)
- [Commits](d3/d3-color@v1.4.1...v3.1.0)

Updates `@decidim/core` from 0.26.8 to 0.28.0
- [Release notes](https://github.com/decidim/decidim/releases)
- [Changelog](https://github.com/decidim/decidim/blob/v0.28.0/CHANGELOG.md)
- [Commits](https://github.com/decidim/decidim/commits/v0.28.0/packages/core)

---
updated-dependencies:
- dependency-name: d3-color
  dependency-type: indirect
- dependency-name: "@decidim/core"
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>