Bump @atlaskit/avatar-group from 12.3.0 to 12.4.0

Bumps [@atlaskit/avatar-group](https://bitbucket.org/atlassian/atlassian-frontend-mirror) from 12.3.0 to 12.4.0.
- [Commits](https://bitbucket.org/atlassian/atlassian-frontend-mirror/commits)

---
updated-dependencies:
- dependency-name: "@atlaskit/avatar-group"
  dependency-version: 12.4.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]