[CI] Fix Pre-commit Issue

[yewentao256]

Purpose

Fix

vllm/v1/worker/gpu_model_runner.py:2386: error: Item "None" of "Any | None" has no attribute "num_draft_tokens"  [union-attr]
vllm/v1/worker/gpu_model_runner.py:2436: error: Item "None" of "Any | None" has no attribute "__iter__" (not iterable)  [union-attr]
vllm/v1/worker/gpu_model_runner.py:2461: error: Item "None" of "Any | None" has no attribute "__iter__" (not iterable)  [union-attr]
Found 3 errors in 1 file (checked 2 source files)

[gemini-code-assist]

Code Review

This pull request addresses several mypy type errors in gpu_model_runner.py. The changes involve adding assert statements to help the type checker understand that certain optional variables are not None in specific code paths, which resolves union-attr errors. Additionally, the type hint for aux_hidden_states has been corrected to Optional[list[torch.Tensor]] to accurately reflect its usage as an iterable. The pull request also includes an improvement to an assertion message in _dummy_run to provide more context during debugging. These changes are correct and improve code quality and maintainability.