### What this PR does / why we need it?
Pin transformers to fix v0.9.1 doctest
### Does this PR introduce _any_ user-facing change?
No
### How was this patch tested?
doctest passed
- vLLM version: v0.10.0
- vLLM main:
c657369841
Signed-off-by: Yikun Jiang <yikunkero@gmail.com>