Numpy deprecation warnings in soiling algorithm

[martin-springer]

Describe the bug
There are a few numpy deprecation warnings left in soiling_cods_test.py

Full error message and traceback
rdtools/test/soiling_cods_test.py: 9322 warnings
/home/runner/work/rdtools/rdtools/rdtools/soiling.py:2219: DeprecationWarning:

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.)

rdtools/test/soiling_cods_test.py: 50 warnings
/home/runner/work/rdtools/rdtools/rdtools/soiling.py:1513: DeprecationWarning:

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.)

rdtools/test/soiling_cods_test.py: 50 warnings
/home/runner/work/rdtools/rdtools/rdtools/soiling.py:1514: DeprecationWarning:

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.)

To Reproduce
Run tests.

Expected behavior
No deprecation warnings.

Additional context
Those warnings should be addressed with the Soiling PR #435.