fix(avatars): use default background surfaceColor with statuses

[geotrev]

Description

Fixes bug introduced in #1885 where Avatar with status defaulted to transparent background.

Before vs. avatar:

Checklist

• :ok_hand: design updates will be Garden Designer approved (add the designer as a reviewer)
• :globe_with_meridians: demo is up-to-date (npm start)
• :arrow_left: renders as expected with reversed (RTL) direction
• :metal: renders as expected with Bedrock CSS (?bedrock)
• [x] :guardsman: includes new unit tests. Maintain existing coverage (always >= 96%)
• :wheelchair: tested for WCAG 2.1 AA accessibility compliance
• :memo: tested in Chrome, Firefox, Safari, and Edge