h52nx: add a warning if the key used for flat-titles is not the expected/recommanded one

3 jobs for rename_ref_titles_to_flat_titles in 2 minutes and 57 seconds (queued for 4 seconds)
Name Stage Failure
failed
test:python3.7-stretch Test
ERROR nxtomomill/io/test/test_config.py
ERROR nxtomomill/io/test/test_confighandler.py
ERROR nxtomomill/io/test/test_frame_group.py
ERROR nxtomomill/io/test/test_io_utils.py
ERROR nxtomomill/test/test_plugins.py
!!!!!!!!!!!!!!!!!!! Interrupted: 13 errors during collection !!!!!!!!!!!!!!!!!!!
============================== 13 errors in 1.45s ==============================
Cleaning up project directory and file based variables
ERROR: Job failed: exit code 1

failed
test:python3.9-buster Test
ERROR nxtomomill/io/test/test_config.py
ERROR nxtomomill/io/test/test_confighandler.py
ERROR nxtomomill/io/test/test_frame_group.py
ERROR nxtomomill/io/test/test_io_utils.py
ERROR nxtomomill/test/test_plugins.py
!!!!!!!!!!!!!!!!!!! Interrupted: 13 errors during collection !!!!!!!!!!!!!!!!!!!
============================== 13 errors in 1.69s ==============================
Cleaning up project directory and file based variables
ERROR: Job failed: exit code 1