Bump @fullhuman/postcss-purgecss from 4.1.3 to 8.0.0

Bumps [@fullhuman/postcss-purgecss](https://github.com/FullHuman/purgecss) from 4.1.3 to 8.0.0.
- [Release notes](https://github.com/FullHuman/purgecss/releases)
- [Changelog](https://github.com/FullHuman/purgecss/blob/main/CHANGELOG.md)
- [Commits](FullHuman/purgecss@v4.1.3...v8.0.0)

---
updated-dependencies:
- dependency-name: "@fullhuman/postcss-purgecss"
  dependency-version: 8.0.0
  dependency-type: direct:development
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

package.json

@@ -110,7 +110,7 @@
     "@ember/test-helpers": "^3.3.1",
     "@ember/test-waiters": "^3.1.0",
     "@embroider/test-setup": "^3.0.3",
-    "@fullhuman/postcss-purgecss": "^4.1.3",
+    "@fullhuman/postcss-purgecss": "^8.0.0",
     "@release-it-plugins/lerna-changelog": "^8.0.1",
     "broccoli-asset-rev": "^3.0.0",
     "chai": "^4.5.0",