Users search: fix avatar size

What does this MR do?

On the users search result page we're requesting 16px images for users' avatars, but rendering them at 40px.

Example search on GitLab.com: https://gitlab.com/search?group_id=9970&project_id=278964&repository_ref=master&scope=users&search=%40dgruzd&snippets=false

This MR fixes this inconsistency.

Screenshots (strongly suggested)

Before

After

Does this MR meet the acceptance criteria?

Conformity

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