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](release-15.0.0...release-15.1.2)

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

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]