Build(deps): Bump xmldom and ember-cli

Removes [xmldom](https://github.com/xmldom/xmldom). It's no longer used after updating ancestor dependency [ember-cli](https://github.com/ember-cli/ember-cli). These dependencies need to be updated together.


Removes `xmldom`

Updates `ember-cli` from 3.15.0 to 3.28.6
- [Release notes](https://github.com/ember-cli/ember-cli/releases)
- [Changelog](https://github.com/ember-cli/ember-cli/blob/v3.28.6/CHANGELOG.md)
- [Commits](ember-cli/ember-cli@v3.15.0...v3.28.6)

---
updated-dependencies:
- dependency-name: xmldom
  dependency-type: indirect
- dependency-name: ember-cli
  dependency-type: direct:development
...

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

Author: dependabot[bot]