Bump knip from 5.18.2 to 5.21.1 (#27)

Bumps [knip](https://github.com/webpro-nl/knip/tree/HEAD/packages/knip) from 5.18.2 to 5.21.1.
- [Release notes](https://github.com/webpro-nl/knip/releases)
- [Changelog](https://github.com/webpro-nl/knip/blob/main/packages/knip/.release-it.json)
- [Commits](https://github.com/webpro-nl/knip/commits/5.21.1/packages/knip)

---
updated-dependencies:
- dependency-name: knip
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

package.json

@@ -40,7 +40,7 @@
     "@types/node": "^20.14.2",
     "chai": "^5.1.1",
     "eslint": "^8.57.0",
-    "knip": "^5.18.2",
+    "knip": "^5.21.1",
     "mocha": "^10.4.0",
     "spellchecker-cli": "^6.2.0",
     "stylelint": "^16.6.1",