setup.sh: fix /etc/sudoers.d permissions

gitlab runs ci jobs with umask 0000 to prevent issues with file
permissions. sudo refuses to look at configuration files in
/etc/sudoers.d if it is world-writable.

Fix these permissions so that sudo still works.
3 jobs for fix-sudoersd-permisions in 1 minute and 2 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed #630
s390x docker-alpine
build-s390x

00:00:52

passed #632
x86 docker-alpine
build-x86

00:01:02

passed #631
x86_64 docker-alpine
build-x86_64

00:00:55