⬆️ Bump xgboost from 1.7.6 to 2.1.1 in /testdata

Bumps [xgboost](https://github.com/dmlc/xgboost) from 1.7.6 to 2.1.1.
- [Release notes](https://github.com/dmlc/xgboost/releases)
- [Changelog](https://github.com/dmlc/xgboost/blob/master/NEWS.md)
- [Commits](dmlc/xgboost@v1.7.6...v2.1.1)

---
updated-dependencies:
- dependency-name: xgboost
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

testdata/requirements.txt

@@ -1,4 +1,4 @@
-xgboost==1.7.6
+xgboost==2.1.1
 scikit-learn==1.4.2
 treelite==3.9.1
 treelite-runtime==3.9.1