Bump @primer/primitives from 7.15.4 to 7.15.5 in /demo

Bumps [@primer/primitives](https://github.com/primer/primitives) from 7.15.4 to 7.15.5.
- [Release notes](https://github.com/primer/primitives/releases)
- [Changelog](https://github.com/primer/primitives/blob/main/CHANGELOG.md)
- [Commits](primer/primitives@v7.15.4...v7.15.5)

---
updated-dependencies:
- dependency-name: "@primer/primitives"
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

demo/package.json

@@ -4,7 +4,7 @@
   "version": "0.1.0",
   "dependencies": {
     "@primer/css": "^21.1.1",
-    "@primer/primitives": "7.15.4",
+    "@primer/primitives": "7.15.5",
     "@rails/actioncable": "^7.1.2",
     "@rails/ujs": "^7.1.2",
     "turbolinks": "^5.2.0",