Bump xgrammar

Bumps the pip group with 1 update in the /api-server/qna-eval directory: [xgrammar](https://github.com/mlc-ai/xgrammar).


Updates `xgrammar` from 0.1.9 to 0.1.18
- [Release notes](https://github.com/mlc-ai/xgrammar/releases)
- [Commits](mlc-ai/xgrammar@v0.1.9...v0.1.18)

---
updated-dependencies:
- dependency-name: xgrammar
  dependency-version: 0.1.18
  dependency-type: direct:production
  dependency-group: pip
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

api-server/qna-eval/requirements.txt

@@ -170,7 +170,7 @@ webencodings==0.5.1
 websockets==14.1
 wrapt==1.17.0
 xformers==0.0.28.post3
-xgrammar==0.1.9
+xgrammar==0.1.18
 yarg==0.1.9
 yarl==1.18.3
 zipp==3.21.0