Fix multi-client tests not writing aggregated results to files

Root cause: Multi-client tests were parsing aggregated JSON from stdout
but never writing it to the expected output file. This caused:
1. full_result_path to remain None
2. Results not being preserved to aggregated results folder
3. Missing JSON files for multi-client tests (e.g., pubsub tests)

Solution: Write the aggregated results_dict to local_benchmark_output_filename
and set full_result_path appropriately, so the file preservation logic works.

Also removed the None check workaround since it was masking the real issue.

redis_benchmarks_specification/__runner__/runner.py

@@ -2885,6 +2885,14 @@ def delete_temporary_files(
                         )
                         results_dict = json.loads(client_container_stdout)
 
+                        # Write aggregated results to file so it can be preserved
+                        full_result_path = local_benchmark_output_filename
+                        with open(full_result_path, "w") as json_file:
+                            json.dump(results_dict, json_file, indent=2)
+                        logging.info(
+                            f"Wrote aggregated multi-client results to {full_result_path}"
+                        )
+
                         # Validate benchmark metrics
                         is_valid, validation_error = validate_benchmark_metrics(
                             results_dict, test_name, benchmark_config, default_metrics
@@ -3101,19 +3109,12 @@ def delete_temporary_files(
                         client_aggregated_results_folder,
                         local_benchmark_output_filename,
                     )
-                    if full_result_path is not None:
-                        logging.info(
-                            "Preserving local results file {} into {}".format(
-                                full_result_path, dest_fpath
-                            )
-                        )
-                        shutil.copy(full_result_path, dest_fpath)
-                    else:
-                        logging.warning(
-                            "No result file path available to preserve for test {}".format(
-                                local_benchmark_output_filename
-                            )
+                    logging.info(
+                        "Preserving local results file {} into {}".format(
+                            full_result_path, dest_fpath
                         )
+                    )
+                    shutil.copy(full_result_path, dest_fpath)
                 overall_result &= test_result
 
                 delete_temporary_files(