Include export commands when running extracted tests

[MatthewBonanni]

In vllm-project/vllm#27683, CI is failing V1 Test attention (B200) because the export VLLM_DISABLE_FLASHINFER_PREFILL=1 command in test-pipeline.yaml is getting ignored. This PR ensures that export commands are run even when specific tests are extracted.

Failing:

commands:
    - export VLLM_DISABLE_FLASHINFER_PREFILL=1
    - pytest -v -s v1/attention

Workaround:

commands:
  - VLLM_DISABLE_FLASHINFER_PREFILL=1 pytest -v -s v1/attention