fix: Handle the case when parameter.required is None and fix tests

PiperOrigin-RevId: 754519323

src/google/adk/tools/openapi_tool/openapi_spec_parser/operation_parser.py

@@ -83,7 +83,8 @@ class OperationParser:
         schema.description = (
             description if not schema.description else schema.description
         )
-        required = param.required
+        # param.required can be None
+        required = param.required if param.required is not None else False
 
         self.params.append(
             ApiParameter(