shell: Ignore failure to hold the scheduler daemon

It’s not fatal, it just means that the daemon might go away while
gnome-software is running.

It returns `G_DBUS_ERROR_FAILED` if the client process (gnome-software)
already has a hold on the daemon, so ignore that completely.

Signed-off-by: Philip Withnall <withnall@endlessm.com>
Status Job ID Name Coverage
  Build
passed #790969
debian-stable-x86_64

00:01:23

failed #790968
fedora-x86_64

00:02:55

 
Name Stage Failure
failed
fedora-x86_64 Build
Uploading artifacts...
_build/config.h: found 1 matching files

_build/meson-logs: found 4 matching files

_build/fedora-x86_64-report.xml: found 1 matching files

Uploading artifacts to coordinator... ok
id=790968 responseStatus=201 Created token=FbcShozp
Uploading artifacts...
_build/fedora-x86_64-report.xml: found 1 matching files

Uploading artifacts to coordinator... ok
id=790968 responseStatus=201 Created token=FbcShozp
ERROR: Job failed: exit code 1