change: restore SKLearn entrypoint customization

Restore entrypoint customization to (one of) the SKLearnProcessor
integration tests, to validate the behavior still works even if
it's not usually required.

Author: athewsey

tests/integ/test_processing.py

@@ -161,6 +161,7 @@ def test_sklearn_with_customizations(
     sklearn_processor = SKLearnProcessor(
         framework_version=sklearn_latest_version,
         role=ROLE,
+        command=["python3"],
         instance_type=cpu_instance_type,
         instance_count=1,
         volume_size_in_gb=100,