Bump esbuild from 0.20.2 to 0.21.4 in /assets

Bumps [esbuild](https://github.com/evanw/esbuild) from 0.20.2 to 0.21.4.
- [Release notes](https://github.com/evanw/esbuild/releases)
- [Changelog](https://github.com/evanw/esbuild/blob/main/CHANGELOG.md)
- [Commits](evanw/esbuild@v0.20.2...v0.21.4)

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

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

assets/package.json

@@ -12,7 +12,7 @@
  "elm": "^0.19.1-6",
  "elm-format": "^0.8.7",
  "elm-test": "^0.19.1-revision12",
- "esbuild": "^0.20.2",
+ "esbuild": "^0.21.4",
  "esbuild-plugin-elm": "^0.0.12",
  "prettier": "^3.2.5",
  "tailwindcss": "^3.4.3"