[CI/CD][V1] Add spec decode tests to CI (#16900)

Signed-off-by: Woosuk Kwon <woosuk.kwon@berkeley.edu>

.buildkite/test-pipeline.yaml

@@ -205,6 +205,7 @@ steps:
     - pytest -v -s v1/sample
     - pytest -v -s v1/worker
     - pytest -v -s v1/structured_output
+    - pytest -v -s v1/spec_decode
     - pytest -v -s v1/test_stats.py
     - pytest -v -s v1/test_utils.py
     - pytest -v -s v1/test_oracle.py