Enable SYCL CPU fallback in CI test containers

[Copilot]

Type

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality).
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Motivation and Context

SYCL tests in GitHub Actions were still skipping the SYCL CPU fallback path because the test process inside the SYCL Docker container did not receive CI=true. As a result, shared C++ and Python test selectors continued to treat SYCL:0 as ignored fallback-only hardware even when no SYCL GPU was available.

Checklist:

• I have run python util/check_style.py --apply to apply Open3D code style
  to my code.
• This PR changes Open3D behavior or adds new functionality.
  • Both C++ (Doxygen) and Python (Sphinx / Google style) documentation is
    updated accordingly.
  • I have added or updated C++ and / or Python unit tests OR included test
    results (e.g. screenshots or numbers) here.
• I will follow up and update the code if CI fails.
• For fork PRs, I have selected Allow edits from maintainers.

Description

• CI propagation into SYCL Docker tests

  • docker/docker_test.sh now forwards CI into SYCL test containers.
  • This activates the existing CI-only fallback logic during actual GitHub test execution, not just on the host runner.

• SYCL test device selection

  • cpp/tests/core/CoreTest.cpp and python/test/open3d_test.py include the SYCL CPU fallback device when:
    • no SYCL GPU is available, and
    • CI is set.
  • Local behavior stays unchanged.

• Hardware-specific SYCL exclusions

  • python/test/t/geometry/test_raycasting_scene.py explicitly opts out of the CI SYCL CPU fallback.
  • Raycasting / Embree tests remain SYCL-GPU-only.

Example:

# Host runner
CI=true docker/docker_test.sh sycl-shared

Inside the container, the shared selectors now see CI=true and can include SYCL:0 for general SYCL tests while keeping raycasting tests off the CPU fallback path.

---

📍 Connect Copilot coding agent with Jira, Azure Boards or Linear to delegate work to Copilot in one click without leaving your project management tool.

[update-docs]

Thanks for submitting this pull request! The maintainers of this repository would appreciate if you could update the CHANGELOG.md based on your changes.