chore(deps): bump scikit-learn pin to 1.8.0 to match basic runtime

The sientia-dev test cluster's "basic" plugin runtime declares
scikit-learn==1.8.0, installed on top of this repo's own
requirements.txt at container startup. The old scikit-learn==1.5.2
pin here got silently overwritten by that later install, but the
son-approx model's pickled LinearRegression wrapper was recreated
against a version needing sklearn 1.8's API — mismatched envs caused
`ImportError: cannot import name 'validate_data' from
sklearn.utils.validation` on model load (found while testing
SIENTIAPDE-1986 against the real cluster). Matching the pin here to
1.8.0 removes the redundant conflicting install.

requirements-local.txt

@@ -15,4 +15,4 @@ hyperopt
 shap
 pycurl
 scipy<1.14.0
-scikit-learn==1.5.2
+scikit-learn==1.8.0

requirements.txt

@@ -15,4 +15,4 @@ hyperopt
 shap
 pycurl
 scipy<1.14.0
-scikit-learn==1.5.2
+scikit-learn==1.8.0