+ X more assignee's icon is not visible on issue board by default

Problem

Currently the grey icon only becomes visible on hover.

see https://gitlab.com/gitlab-org/gitlab-ce/issues/33409 for example

Solution

quoting from: https://gitlab.com/gitlab-org/gitlab-ee/issues/1904

If there are 4 assignees, we can show them all, and if there are more than 4, we can use the fourth circle to indicate the number of remaining assignees

So the fourth grey circle with the number should be visible if more than 4 assignees..

@ClemMakesApps assigned this to you, as you worked on the original issue 😉