Add govulncheck to CI

[julio-lopez]

It'd be good to add govulncheck as part of the PR verification and CI processes.

Here is how it was done in the upstream kopia project: kopia/kopia@d637814

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[Jayanth-Parthsarathy]

Hey @pavannd1 @julio-lopez . I would love to work on this. Can you please assign this to me?