[Vertical Privilege Escalation] User can Unapproved any Approved Translation at [/translations/unapprove/]

Hi, team. During testing, I discovered that only privileged users or translation owners can unapprove an approved translation, but due to logical errors, any logged-in user can unapprove any approved translation.

Steps To Reproduce:

• Go to https://mozilla-pontoon-staging.herokuapp.com/ and log in to your account.

• Click on Teams and select any team from the menu.