[ci] Sync test areas with test-pipeline.yaml and enable new pipeline generator (#33080)

Signed-off-by: Kevin H. Luu <khluu000@gmail.com>
Signed-off-by: khluu <khluu000@gmail.com>
Co-authored-by: Kevin Luu <khluu@Kevins-MacBook-Pro.local>

.buildkite/test_areas/engine.yaml

@@ -23,4 +23,8 @@ steps:
     # TODO: accuracy does not match, whether setting
     # VLLM_USE_FLASHINFER_SAMPLER or not on H100.
     - pytest -v -s v1/e2e
-    - pytest -v -s v1/engine
+    # Run this test standalone for now;
+    # need to untangle use (implicit) use of spawn/fork across the tests.
+    - pytest -v -s v1/engine/test_preprocess_error_handling.py
+    # Run the rest of v1/engine tests
+    - pytest -v -s v1/engine --ignore v1/engine/test_preprocess_error_handling.py