[Bugfix] Pin xgrammar to 0.1.11

[mgoin]

There seems to be an breaking change to the apply_token_bitmask_inplace_cuda op in the latest release of xgrammar 0.1.13, so let's pin for now to fix

https://vllm-dev.slack.com/archives/C07R5PAL2L9/p1739652025939989?thread_ts=1739650060.428689&cid=C07R5PAL2L9

[2025-02-15T00:55:01Z]   File "/usr/local/lib/python3.12/dist-packages/vllm/model_executor/guided_decoding/xgrammar_decoding.py", line 343, in __call__
[2025-02-15T00:55:01Z]     xgr.apply_token_bitmask_inplace(
[2025-02-15T00:55:01Z]   File "/usr/local/lib/python3.12/dist-packages/xgrammar/matcher.py", line 133, in apply_token_bitmask_inplace
[2025-02-15T00:55:01Z]     apply_token_bitmask_inplace_cuda(logits, bitmask, indices)
[2025-02-15T00:55:01Z]   File "/usr/local/lib/python3.12/dist-packages/xgrammar/kernels/apply_token_bitmask_inplace_cuda.py", line 77, in apply_token_bitmask_inplace_cuda
[2025-02-15T00:55:01Z]     torch.ops.xgrammar.apply_token_bitmask_inplace_cuda(logits, bitmask, indices)
[2025-02-15T00:55:01Z]   File "/usr/local/lib/python3.12/dist-packages/torch/_ops.py", line 1116, in __call__
[2025-02-15T00:55:01Z]     return self._op(*args, **(kwargs or {}))
[2025-02-15T00:55:01Z]            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[2025-02-15T00:55:01Z] RuntimeError: bitmask must have the hidden size equal to ceilDiv(vocabSize, 32).

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cc @russellb