dh_setup_copyright: Don't use the apt cache to find source package names

The OBS builders don't have any source lists set up, so apt-cache showsrc never finds any results. Instead, we can rely on dpkg-query to extract the info, along with some adjustments to get the correct version value.

https://phabricator.apertis.org/T9756

Signed-off-by: Ryan Gonzalez ryan.gonzalez@collabora.com