### What this PR does / why we need it?
Fix ngram precision issue and open e2e ngram test
- vLLM version: v0.11.0
- vLLM main:
83f478bb19
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Signed-off-by: Icey <1790571317@qq.com>
Signed-off-by: zhaomingyu <zhaomingyu13@h-partners.com>
Co-authored-by: Icey <1790571317@qq.com>