Fix some speculative decode tests with tl.dot

[huydhn]

I'm seeing these failures from my other PR #16859, but they don't seem to be related to PyTorch 2.7.0 release. They seem to come from #13305 with the issue on Triton triton-lang/triton#2266. I have seen similar a PR from PyTorch about this pytorch/pytorch#147765.

The PR attempts to fix the failed tests accordingly.

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[huydhn]

This fixes some spec decode failures but not all of them. Specifically, https://github.com/vllm-project/vllm/blob/main/.buildkite/test-pipeline.yaml#L283 has been fixed, but there are more failures from the next line VLLM_ATTENTION_BACKEND=FLASH_ATTN pytest -v -s spec_decode --ignore=spec_decode/e2e/test_multistep_correctness.py --ignore=spec_decode/e2e/test_mtp_correctness.py. I have been debugging them and the root cause points to #17084. cc @WoosukKwon