Conversion of an array with ndim > 0 to a scalar is deprecated

[jakirkham]

Noticing this warning on CI:

hdbscan/tests/test_flat.py::test_flat_base_default PASSED                [  1%]
##[warning]Conversion of an array with ndim > 0 to a scalar is deprecated, and will error in future. Ensure you extract a single element from your array before performing this operation. (Deprecated NumPy 1.25.)
...
hdbscan/tests/test_flat.py::test_approx_predict_default PASSED           [  6%]
##[warning]Conversion of an array with ndim > 0 to a scalar is deprecated, and will error in future. Ensure you extract a single element from your array before performing this operation. (Deprecated NumPy 1.25.)
...

[jakirkham]

Looks like we may need the patch in comment: #646 (comment)