Run ONNX model tests as part of pkgci_test_onnx.

[ScottTodd]

Progress on iree-org/iree-test-suites#6.

Current tests included and their statuses:

PASSED onnx_models/tests/vision/classification_models_test.py::test_alexnet
PASSED onnx_models/tests/vision/classification_models_test.py::test_caffenet
PASSED onnx_models/tests/vision/classification_models_test.py::test_densenet_121
PASSED onnx_models/tests/vision/classification_models_test.py::test_googlenet
PASSED onnx_models/tests/vision/classification_models_test.py::test_inception_v2
PASSED onnx_models/tests/vision/classification_models_test.py::test_mnist
PASSED onnx_models/tests/vision/classification_models_test.py::test_resnet50_v1
PASSED onnx_models/tests/vision/classification_models_test.py::test_resnet50_v2
PASSED onnx_models/tests/vision/classification_models_test.py::test_shufflenet
PASSED onnx_models/tests/vision/classification_models_test.py::test_shufflenet_v2
PASSED onnx_models/tests/vision/classification_models_test.py::test_squeezenet
PASSED onnx_models/tests/vision/classification_models_test.py::test_vgg19
XFAIL onnx_models/tests/vision/classification_models_test.py::test_efficientnet_lite4
XFAIL onnx_models/tests/vision/classification_models_test.py::test_inception_v1
XFAIL onnx_models/tests/vision/classification_models_test.py::test_mobilenet
XFAIL onnx_models/tests/vision/classification_models_test.py::test_rcnn_ilsvrc13
XFAIL onnx_models/tests/vision/classification_models_test.py::test_zfnet_512

• CPU only for now. We haven't yet parameterized those tests to allow for other backends or flags.
• Starting with --override-ini=xfail_strict=false so newly passing tests won't fail the job. Newly failing tests will fail the job. We can add an external config file to customize which tests are expected to fail like the onnx op tests if we want to track which are passing/failing in this repository instead of in the test suite repo.

Sample logs: https://github.com/iree-org/iree/actions/runs/11371239238/job/31633406729?pr=18795

ci-exactly: build_packages, test_onnx

[saienduri]

Thanks, yeah would be nice to have a way to control the xfail configs here in iree itself