libdescriptor not available for macOS

[mjwen]

Adding libdescritpor as a dependence causes CI test to fail, because it is not available for macOS for now. See https://github.com/openkim/kliff/actions/runs/8026351667

This is mainly because neither wheel or source is available for macOS.

Waiting for https://github.com/openkim/libdescriptor/issues/4

[mjwen]

Based on https://github.com/openkim/libdescriptor/issues/4, installing libdescriptor on Mac can be tricky. So for now, the best way to move forward is to disable testing on macOS in the CI. Once @ipcamit figured that out. We will re-enable testing on macOS.