Bump @umbraco-cms/backoffice in /src/Umbraco.Web.UI.Login

Bumps [@umbraco-cms/backoffice](https://github.com/umbraco/Umbraco-CMS) from 15.0.0 to 15.1.2.
- [Release notes](https://github.com/umbraco/Umbraco-CMS/releases)
- [Commits](https://github.com/umbraco/Umbraco-CMS/compare/release-15.0.0...release-15.1.2)

---
updated-dependencies:
- dependency-name: "@umbraco-cms/backoffice"
  dependency-type: direct:development
...

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

src/Umbraco.Web.UI.Login/package.json

@@ -14,7 +14,7 @@
   },
   "dependencies": {},
   "devDependencies": {
-    "@umbraco-cms/backoffice": "^15.0.0",
+    "@umbraco-cms/backoffice": "^15.1.2",
     "msw": "^2.6.4",
     "typescript": "^5.6.3",
     "vite": "^5.4.11",