build(deps): bump immutable from 4.3.4 to 4.3.8 in /webui

Bumps [immutable](https://github.com/immutable-js/immutable-js) from 4.3.4 to 4.3.8.
- [Release notes](https://github.com/immutable-js/immutable-js/releases)
- [Changelog](https://github.com/immutable-js/immutable-js/blob/main/CHANGELOG.md)
- [Commits](immutable-js/immutable-js@v4.3.4...v4.3.8)

---
updated-dependencies:
- dependency-name: immutable
  dependency-version: 4.3.8
  dependency-type: indirect
...

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

Author: dependabot[bot]