Malformed Avatar URL in boards filter bar

The boards route being monitored for our LCP leaderboard is currently one of the slowest routes.

Looking at this sitespeed report we can see a redirect to sign in happens in the waterfall.

We seem to be loading a malformed URL/Avatar on the boards (https://gitlab.com/groups/gitlab-org/-/boards/1235826?label_name[]=devops%3A%3Aplan&label_name[]=group%3A%3Aproject%20management) which ends up as a 404 (in our performance monitoring it is a 503 as that user is not logged in)

Resolving this should lead to a more accurate LCP for the performance measurements so we can establish a better baseline for future improvements.

Steps to reproduce

1. With the browser network tab open, load https://gitlab.com/groups/gitlab-org/-/boards/1235826?label_name[]=devops%3A%3Aplan&label_name[]=group%3A%3Aproject%20management
2. You will see a 404 network request to https://gitlab.com/groups/gitlab-org/-/boards/%7B%7Bavatar_url%7D%7D

Possible fixes

@engwan identified that it looks like this is coming from the filter bar, but noted that we use a similar filter bar on issue list which doesn't have this problem.

= render 'shared/issuable/user_dropdown_item',
      user: User.new(username: '{{username}}', name: '{{name}}'),
      avatar: { lazy: true, url: '{{avatar_url}}' }