The `ostruct` ruby gem relied on for embedded ruby code execution is being removed

[aramprice]

See https://github.com/cloudfoundry/bosh-cli/actions/runs/19979887824/job/57304254066?pr=707#step:5:22 for example of failure

Ruby 3.5 / 4.0 is not yet finalized and things may change but if ostruct is removed from the standard gems the CLI will no longer be able to rely on it being present when invoking ruby.

See also: #707