CE does support restricting branches to specific roles: Master and Developer. In your case, I would suggest giving this single maintainer the Master role (which

CE does support restricting branches to specific roles: Master and Developer. In your case, I would suggest giving this single maintainer the Master role (which they already have if they're the owner of the project), making everyone else a Developer and configuring the master branch to only allow pushes (and merges) from Masters.