ui: bump sass from 1.90.0 to 1.91.0 in /ui

Bumps [sass](https://github.com/sass/dart-sass) from 1.90.0 to 1.91.0.
- [Release notes](https://github.com/sass/dart-sass/releases)
- [Changelog](https://github.com/sass/dart-sass/blob/main/CHANGELOG.md)
- [Commits](sass/dart-sass@1.90.0...1.91.0)

---
updated-dependencies:
- dependency-name: sass
  dependency-version: 1.91.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]