WinML tests have implicit dependency on `--enable_onnx_tests` being specified

Describe the bug
If --use_winml is specified when building ONNX Runtime but --enable_onnx_tests is not, the build will fail when it attempts to run the WinML unit tests due to setup_test_data not having been called to create the 'models' directory

https://github.com/microsoft/onnxruntime/blob/bed6e87cbdbe1120f7958b6e1eeff5eda3c11e8e/tools/ci_build/build.py#L2051-L2052

and the WinML test setup code throwing if that directory does not exist

https://github.com/microsoft/onnxruntime/blob/e344a583b0f39c6b8aca57f61b957022f45ec047/winml/test/model/model_tests.cpp#L151

Urgency
None.

System information

• ONNX Runtime installed from (source or binary): source
• ONNX Runtime version: master

Expected behavior
Implicit dependency should be enforced when validating build.py arguments, or removed if having a 'models' directory is not required. The calling code would suggest that a non-existent directory was permissible at some point.

https://github.com/microsoft/onnxruntime/blob/e344a583b0f39c6b8aca57f61b957022f45ec047/winml/test/model/model_tests.cpp#L175-L176