Unlimit xgboost version

**What's your use case?**

It seems that the latest `xgboost` MacOS package is missing `libomp.dylib`.
Therefore the xgboost version has been limited in #6857 to <2.1.

**What's your proposed solution?**

Unlimit the xgboost version when the issue is fixed on the xgboost side.

**Are there any alternative solutions?**
Instal libomp manually and move xgboost to optional requirements.

Start by reading issue #6857 and checking the current xgboost dependency constraint in the repository. Verify whether the macOS package now includes libomp.dylib or otherwise installs successfully without manual intervention. Done means the version restriction can be removed without breaking macOS installation.

Written by the indexing model from the issue text.