[ROCm] pass AMD test commands via VLLM_TEST_COMMANDS env var to fix quoting

[AndreasKaratzas]

AMD mirror steps fail with /bin/sh: 1: Syntax error: "(" unexpected before run-amd-test.sh even executes. This affects any test step with pytest marker expressions like -m 'core_model and (not slow_test)'.

The pipeline generator's _prepare_commands converts single quotes to double quotes and injects CUDA_COREDUMP_GENERATION_FLAGS="skip_...". When these are passed as a positional argument wrapped in outer double quotes:

bash run-amd-test.sh "... CUDA_COREDUMP_GENERATION_FLAGS="skip_..." && ... -m "core_model and (not slow_test)""

Fix

Pass commands via the VLLM_TEST_COMMANDS environment variable instead of as a positional argument. Buildkite sets env vars directly in the process environment without shell interpretation, so all inner quoting is preserved.

Motivation

• [ROCm][CI] Added MI325 mirrors (stage C) vllm#35239
• https://buildkite.com/vllm/ci/builds/53841/steps/canvas?sid=019ca61a-74dc-4b20-8198-fd2a5dea3d4a&tab=output

cc @kenroche

[khluu]

is this change meant for CI or AMD CI?

[AndreasKaratzas]

I think it addresses a failure mostly on CI, and not AMD CI. So far AMD CI does not have that failure. However I was thinking of modifying the relative part on AMD CI as well.