Bump reffy from 18.3.2 to 18.4.0 (#1476)

Bumps [reffy](https://github.com/w3c/reffy) from 18.3.2 to 18.4.0.
- [Changelog](https://github.com/w3c/reffy/blob/main/CHANGELOG.md)
- [Commits](https://github.com/w3c/reffy/commits)

---
updated-dependencies:
- dependency-name: reffy
  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>

Author: dependabot[bot]

package-lock.json

@@ -36,7 +36,7 @@
     "css-tree": "3.1.0",
     "flags": "0.2.2",
     "mocha": "11.1.0",
-    "reffy": "18.3.2",
+    "reffy": "18.4.0",
     "rimraf": "6.0.1",
     "strudy": "^3.1.1",
     "webidl2": "24.4.1"