Python tests: fix tests flag (#28298)

* Tests flag got missed in the config

TEST: tested with --tests flag, saw only requested test run

* python: proof why we need stronly typed languages

src/python_testing/matter_testing_support.py

@@ -818,6 +818,7 @@ def convert_args_to_matter_config(args: argparse.Namespace) -> MatterTestConfig:
     config.paa_trust_store_path = args.paa_trust_store_path
     config.ble_interface_id = args.ble_interface_id
     config.pics = {} if args.PICS is None else read_pics_from_file(args.PICS)
+    config.tests = [] if args.tests is None else args.tests
 
     config.controller_node_id = args.controller_node_id
     config.trace_to = args.trace_to