Simplify test logic

[onedr0p]

There is a limitation on goss when testing a container and having an ENTRYPOINT like this:

ENTRYPOINT ["/usr/bin/catatonit", "--", "/entrypoint.sh"]

Goss will attempt to run the container and it will likely fail because the entrypoint.sh will never exit 0

I suggest to make the tests a simple toggle to enable / disable, e.g.

app: postgres-init
semver: true
test: false
channels:
  - name: stable
    platforms: ["linux/amd64", "linux/arm64"]
    stable: true