Resolve invalid reference for avatar url

[JasonBristol]

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• [x] I have tested my changes against the review branch (the latest developmental version), and this pull request is targeting that branch as a base
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Description

This PR resolves an invalid reference to avatar url

AttributeError: 'ClientUser' object has no attribute 'avatar_url'

Related issues (if applicable)

#2294 #2290

[zpammer]

Works, thx!