fix: anthropic max token NoneType error (#6858)

api/core/model_runtime/model_providers/anthropic/llm/claude-3-5-sonnet-20240620.yaml

@@ -26,6 +26,7 @@ parameter_rules:
     required: false
   - name: max_tokens
     use_template: max_tokens
+    required: true
     default: 8192
     min: 1
     max: 8192