Bump @types/leaflet from 1.9.12 to 1.9.15 in /front-end

Bumps [@types/leaflet](https://github.com/DefinitelyTyped/DefinitelyTyped/tree/HEAD/types/leaflet) from 1.9.12 to 1.9.15.
- [Release notes](https://github.com/DefinitelyTyped/DefinitelyTyped/releases)
- [Commits](https://github.com/DefinitelyTyped/DefinitelyTyped/commits/HEAD/types/leaflet)

---
updated-dependencies:
- dependency-name: "@types/leaflet"
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

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

front-end/package.json

@@ -26,7 +26,7 @@
   "devDependencies": {
     "@rushstack/eslint-patch": "^1.10.4",
     "@tsconfig/node20": "^20.1.4",
-    "@types/leaflet": "^1.9.12",
+    "@types/leaflet": "^1.9.15",
     "@types/node": "^22.7.4",
     "@typescript-eslint/eslint-plugin": "^7.18.0",
     "@typescript-eslint/parser": "^7.18.0",