power: Lock screen when the lid is closed without external monitors

We currently only lock the screen when suspend is disabled on the
session level. This is somewhat ironic, because in reality suspend
happens because of systemd-logind.

In the case where we suspend, it does not hurt to also explicitly lock
the screen. In the case that suspend is inhibited (through GNOME
Tweaks), this fixes issues where the session remains unlocked.

See also #88
and gnome-tweaks!33
Status Job ID Name Coverage
  Build
passed #222316
build

00:00:32

 
  Test
passed #222317
test

00:01:25

 
  Manual
manual #222318
allowed to fail manual
asan
manual #222321
allowed to fail manual
msan
manual #222319
allowed to fail manual
tsan
manual #222320
allowed to fail manual
ubsan