Remove scikit-learn version restriction < 1.6

[martin-springer]

Describe the bug
Looks like scikit-learn just had a new release (https://scikit-learn.org/stable/whats_new/v1.6.html#version-1-6-0) and introduced a new tag sklearn_tags that seems to not yet work with xgboost.

Full error message and traceback
FAILED rdtools/test/filtering_test.py::test_xgboost_clip_filter - AttributeError: 'super' object has no attribute 'sklearn_tags'

To Reproduce
Run pytests with update strategy eager (as of 12/12/2024).

Expected behavior
No failed tests.

Additional context
This bug is most likely going to be fixed with the next update of xgboost and is mostly a reminder to remove the version restriction.

[martin-springer]

xgboost is aware of the issue: dmlc/xgboost#11093