build(deps-dev): bump workbox-webpack-plugin in /build/frontend-legacy

Bumps [workbox-webpack-plugin](https://github.com/googlechrome/workbox) from 7.3.0 to 7.4.0.
- [Release notes](https://github.com/googlechrome/workbox/releases)
- [Commits](https://github.com/googlechrome/workbox/compare/v7.3.0...v7.4.0)

---
updated-dependencies:
- dependency-name: workbox-webpack-plugin
  dependency-version: 7.4.0
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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

build/frontend-legacy/package.json

@@ -136,7 +136,7 @@
     "webpack": "^5.103.0",
     "webpack-cli": "^6.0.1",
     "webpack-merge": "^6.0.1",
-    "workbox-webpack-plugin": "^7.3.0"
+    "workbox-webpack-plugin": "^7.4.0"
   },
   "engines": {
     "node": "^24.0.0",