De-emphasize nested reports in MR widget

What does this MR do?

Related to #293655 (closed)

De-emphasizes nested reports in the test report MR widget by

• Indenting the child test results using a left padding of 2.5rem.
• Reducing the child results item container height reduced from .625rem to .5rem.
• Reducing the status icon in the child container dimensions to from 24px/2rem to 16px/1rem.
• If a child container displays a warning state, the background color is now $gray-10 - the same as the scrollable container.

Screenshots (strongly suggested)

Before

After

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team