Append to .out files for pre-emptable finalize job

src/xfel_calibrate/calibrate.py

@@ -611,6 +611,7 @@ def run_finalize(fmt_args, temp_path, job_list, sequential=False):
             '--parsable',
             '--requeue',
             '--output', f'{temp_path}/slurm-%j.out',
+            '--open-mode=append',  # So we can see if it's preempted & requeued
             '--job-name', 'xfel-cal-finalize',
             '--time', finalize_time_limit,
             '--partition', 'exfel',