Add missing generic arguments in engine tests to fix valac criticals

See vala#835
5 jobs for wip/ricotz/criticals in 33 minutes and 7 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
failed #392874
fedora

00:01:32

passed #392875
ubuntu

00:33:07

 
  Test
skipped #392876
flatpak
 
  Deploy
skipped #392877
review
skipped #392878
allowed to fail manual
stop_review
 
Name Stage Failure
failed
fedora Build
 Problem: conflicting requests
- nothing provides pkgconfig(telepathy-glib) >= 0.19.9 needed by folks-devel-1:0.13.1-2.fc31.i686
- nothing provides pkgconfig(telepathy-glib) >= 0.19.9 needed by folks-devel-1:0.13.1-2.fc31.x86_64
(try to add '--skip-broken' to skip uninstallable packages)
Uploading artifacts...
WARNING: build/meson-logs/meson-log.txt: no matching files
WARNING: build/meson-logs/testlog.txt: no matching files
ERROR: No files to upload
ERROR: Job failed: exit code 1