[Task]: Run the validation suite in CI as a non-blocking job

[michael-duren]

What needs to be done

Run the validation suite in CI (GitHub Actions) as a non-blocking job so we
can watch conformance evolve without red-gating active development.

The job should:

• Run on a Linux runner with the kernel features the runtime needs (namespaces,
  cgroups v2). Note runner limitations (e.g. user-namespace / rootless constraints).
• Build box and run make validation.
• Be marked non-required / continue-on-error so a partially-red suite doesn't
  block merges during this epic.
• Upload the suite output (TAP / summary) as a build artifact for inspection.

Acceptance criteria

• A GitHub Actions workflow runs the validation suite on push/PR
• The job is non-blocking (continue-on-error or not a required check)
• Suite output is uploaded as an artifact
• Any runner/kernel limitations affecting which tests can run are documented
• The workflow is green-or-neutral even while individual validation tests fail

Parent / tracking issue

Part of the OCI runtime validation epic.

Blocked by

• Add a local make validation target to run the suite against box

Rough size

M — a day or two