main: Don't show welcome dialogue for Live CD users

Fedora uses a 'liveuser' user for its "Live CD" Workstation
installation. Don't show a welcome tour, otherwise we'd show it every
start.

Closes: #3729
11 jobs for !1677 with wip/hadess/liveuser-no-tour in 3 minutes and 6 seconds (queued for 2 seconds)
detached
Status Job ID Name Coverage
  Pre Review
passed #1155856
check_commit_log

00:00:30

passed #1155857
check-merge-request

00:00:23

 
  Prep
passed #1155858
build-fedora-container

00:00:32

 
  Review
passed #1155860
eslint

00:01:25

passed #1155861
eslint_mr

00:01:03

passed #1155859
js_check

00:00:24

passed #1155863
no_template_check

00:00:17

passed #1155862
potfile_check

00:00:15

 
  Build
passed #1155864
build

00:01:51

passed #1155865
flatpak
flatpak

00:01:26

 
  Test
passed #1155866
test

00:00:43