Avatar > Stacked (inline) avatars > Update to match new Figma specs

### Description

The stacked (inline) avatar component was [recently updated in Figma](https://gitlab.com/gitlab-org/gitlab-services/design.gitlab.com/-/issues/1104).

Subsequently, https://gitlab-org.gitlab.io/gitlab-ui/?path=/story/base-avatar-avatars-inline--default also needs updating to match the new style.

#### Figma file

<!-- If design specs exist in Figma, link them below. Otherwise, remove the link and add a link to the issue to add the component to Figma -->

[View design specs in Figma →](https://www.figma.com/file/qEddyqCrI7kPSBjGmwkZzQ/Component-library?node-id=1833%3A2791)

### Checklist

Make sure the following are completed before closing the issue:

1. [x] Assign the correct component label to this issue.
1. [ ] Create an MR with the additions or updates needed.
1. [ ] Be sure to get your MR reviewed by a [FE/UX Foundations designer][foundations-team].
1. [ ] When applicable, update `followsDesignSystem:` with the correct value inside the `[component].documentation.js` file.
1. [ ] When applicable, create an [MR in Pajamas][pajamas-mr] to update the demos. If you do not have capacity to complete the demos, [create an issue in Pajamas][pajamas-issue] and bring the issue to your team planning session for prioritization and scheduling. Mark the issue as related to this one.
1. [ ] When applicable, [create an MR in Pajamas][pajamas-mr] to update the component status.
1. [ ] When applicable, [create an issue in Pajamas][pajamas-issue] using the ["Component Documentation"][pajamas-component-documentation-template] issue template to update guidelines. Ping a designer on your team for awareness and bring the issue to your team planning meeting for prioritization and scheduling.
1. [x] When applicable, [create an issue in Pajamas][pajamas-issue] using the ["Figma update"][pajamas-figma-update-template] issue template to update the Figma UI Kit. Ping a designer on your team for awareness and bring the issue to your team planning meeting for prioritization and scheduling.
1. [ ] When introducing a major or breaking change, communicate the changes within the [Engineering Week in Review][eng-week-in-review-doc].
1. [ ] 🎉 Congrats, you made it! You can now close this issue.

<!-- 
### Resources

* [Compontent Lifecycle][component-lifecycle]
* [Adding component][adding-components]
* [Adding CSS][adding-css]
* [Breaking changes][breaking-changes]
-->

[foundations-team]: https://about.gitlab.com/company/team/?department=fe-ux-foundations-team
[pajamas-mr]: https://gitlab.com/gitlab-org/gitlab-services/design.gitlab.com/-/merge_requests/new
[pajamas-issue]: https://gitlab.com/gitlab-org/gitlab-services/design.gitlab.com/-/issues/new
[pajamas-component-documentation-template]: https://gitlab.com/gitlab-org/gitlab-services/design.gitlab.com/-/issues/new?issuable_template=Component%20documentation
[pajamas-figma-update-template]: https://gitlab.com/gitlab-org/gitlab-services/design.gitlab.com/-/issues/new?issuable_template=Figma%20update
[component-lifecycle]: https://design.gitlab.com/get-started/lifecycle
[adding-components]: https://gitlab.com/gitlab-org/gitlab-ui/-/blob/main/doc/contributing/adding_components.md
[adding-css]: https://gitlab.com/gitlab-org/gitlab-ui/-/blob/main/doc/contributing/adding_css.md
[breaking-changes]: https://gitlab.com/gitlab-org/gitlab-ui/-/blob/main/doc/contributing/breaking_changes_to_components.md
[eng-week-in-review-doc]: https://docs.google.com/document/d/1GQbnOP_lr9KVMVaBQx19WwKITCmh7H3YlgO-XqVwv0M/edit

Story points: 1.0