Fix avatar rendering in projects and groups navigation

What does this MR do?

The avatar on projects and groups navigation dropdown are stretched to fit into a square even though the image might not be a square.

The fix is just add missing class to the html element.

Related issue: #196870 (closed)

Screenshots

Tested with ubuntu logo:

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
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• 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

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• 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
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