ci: add vulnerability checks

[gfelbing]

Currently, for an outside user I cannot see if there is a vulnerability check (e.g. snyk) in place.
Please consider adding it and/or make it transparent.

[cgoetz-inovex]

Hi @gfelbing,
thanks for your reuqest, I've created an internal issue to integrate govulncheck into CI and add a link to the results into the readme.