ci(e2e): less ginkgo output (#955)

The `e2e.test` binary has __all__ kubernetes tests, but we only run
those that start with `External.Storage`. This means there is a lot of
"Skipped" output right now, that is useless. By setting
`--silence-skips` these log lines are removed.

Additional ginkgo offers a `--github-output` flag that promises to make
the output nicer for GitHub actions. Not sure what it really does.

These flags are only supported in Ginkgo 2.18+, which is only available
in Kubernetes 1.31+.