To run integration tests we build an rpm package locally with osc and install
this by calling `zypper --non-interactive in <local_package_path>`.

This process does not work anymore in the latest Tumbleweed snapshots because
zypper requires an existing signature unless the parameter `--no-gpg-checks` is
provided.

But using `--no-gpg-checks` would be a security risk because all the
dependencies are then also not verified and often downloaded via http. Before
the change they were verified so tampering was not possible.

To prevent those security risks it would be great if locally available packages
can still be installed non-interactively without disabling the gpg checks.