ATR-28398: Fix nested containers for transform substeps

Another follow up of !66655 (merged).
Cover case of a transform substep running within a container, when the transform itself runs within a container on the Grid. Up to now, nested containers worked locally and in CI, but not on the Grid, due to differences in the job setup. Thanks to @desilva, @walkerr, @aforti for helping understanding better the details of the container jobs setup. Tagging @tadej, @jcatmore, @jchapman, @nstyles.