While the test was correct and checked if there is only
`record.db` in a given dir (and no other files) it wouldn't
tell us whether the file wasn't there or there were additional
files found. Hence replace the test by assertions that tell
use exactly what failed easing debugging in CI.
Fixes: e4bd4580 ("tests: Add application shutdown tests")
Signed-off-by: Guido Günther <agx@sigxcpu.org>
Part-of: <https://gitlab.gnome.org/GNOME/calls/-/merge_requests/795>