Fix accessibility on avatars links

[Stef-Rousset]

🎩 What? Why?

This PR allows avatars links to be accessible when navigating with Voice Over or another screen reader.
This PR is issued from the audit of Angers city (page 21) and is rrlatd to criterias critères 1.4.1 and R.4.7 from WCAG.

📌 Related Issues

Github card https://github.com/orgs/OpenSourcePolitics/projects/26/views/1?pane=issue&itemId=112401383&issue=OpenSourcePolitics%7Cintern-tasks%7C25

Testing

1. As a user, enable Voice Over
2. On processes index page, click on the home icon to open the dropdown menu
3. Navigate with voice over in the menu and see that the focus is well displayed on avatars links and that you can access them (cf screenshot one)
4. Go to the show of a proposal and navigate with voice over on the page, see that the avatar link gets the focus and that you can access it (cf screenshot two)

📷 Screenshots (optional)

ONE

TWO

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions. @carolromero & @xabier feel free to chime in.