test: Add a simple test for listing target versions in sysupdate

I’m about to refactor it slightly and it would be nice to have a little
test coverage to check against.

(cherry picked from commit 8433ed1c7a66ee575621cde027a890017769252c)

test/units/TEST-72-SYSUPDATE.sh

@@ -692,6 +692,10 @@ EOF
         exit 1
     fi
 
+    # Check that the target versions are listed correctly.
+    [[ $( "$SYSUPDATE" --verify=no --json=short list | jq -cr '.all') == '["v9","v8","v7","v6","v5","v3","v2","v1"]' ]]
+    [[ $( "$SYSUPDATE" --verify=no --offline --json=short list | jq -cr '.all') == '["v9","v8","v7","v6"]' ]]
+
     # Cleanup
     [[ -b "$blockdev" ]] && losetup --detach "$blockdev"
     rm "$BACKING_FILE"