[BUG] Failed update of contributor renders all contributors instead of active contributors

[mattwr18]

Steps to reproduce

• Deactivate a contributor locally
• Visit another contributor's show page, ie /contributors/5
• Upload a avatar with a file type that is not allowed, ie .pdf, .csv... by clicking on Profilbild ändern
• Page is re-rendered with an error flash advising that the update failed
• See that the deactivated contributor is in the list in the contributors sidebar aside. (this would happen with unsubscribed contributors as well)

Dev Notes

This occurs because in the ContributorsController#update method, the instance variable @contributors is set to all contributors and not filtered as it is in the show method