Python: Add class validation for Dapr Runtime step loading #28416

Job	Run time
paths-filter	10s
python-integration-tests-check	7s
Python Pre-Merge Integration Tests - Memory (incl samples using those)	0s
Python Pre-Merge Integration Tests - Multi-Modality	0s
Python Pre-Merge Integration Tests - Ollama	0s
Python Pre-Merge Integration Tests - Agents	0s
Python Pre-Merge Integration Tests - AI Services (incl samples using those)	0s
Python Integration Tests - Scheduled run	0s
	17s

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