Tests emit `FutureWarning` from `skimage`

[kandersolar]

From https://github.com/pvlib/pvanalytics/actions/runs/16749387378/job/47415518403#step:5:48

pvanalytics/tests/features/test_shading.py::test_fixed_no_shadows
pvanalytics/tests/features/test_shading.py::test_fixed_same_index
pvanalytics/tests/features/test_shading.py::test_simple_shadow
  /Users/runner/work/pvanalytics/pvanalytics/pvanalytics/features/shading.py:368: FutureWarning: `rectangle` is deprecated since version 0.25 and will be removed in version 0.27. Use `skimage.morphology.footprint_rectangle` instead.
    three_minute_mask = morphology.rectangle(1, 3)