backup with --concurrency=X and --skip-if-no-change will fail if nothing changed

if running an inc backup with --concurrency=x and --skip-if-no-change and nothing has changed, backup will fail with:

/ $ /usr/local/bin/duplicity --encrypt-key=C14B3DABD0E9E5DDA325312A1FC7A49EF417B70D inc --s3-use-glacier-ir --allow-source-mismat
ch --exclude '**/*.$.jpg' --exclude '**/.@__thumb' --exclude '**/.dtrash' --exclude '**/.streams' --exclude '**/.DS_Store' --excl
ude '**/@Recycle' --jsonstat --concurrency 3 --skip-if-no-change /mnt/mydata/2000 s3:///duplicity-photo/photo-weekly/2000
Local and Remote metadata are synchronized, no sync needed.
Last full backup date: Mon Jun 19 06:50:08 2023
Skipped volume upload, as effectivly nothing has changed
Traceback (innermost last):
  File "/usr/local/lib/python3.11/site-packages/duplicity/__main__.py", line 62, in dup_run
    with_tempdir(main)
  File "/usr/local/lib/python3.11/site-packages/duplicity/__main__.py", line 53, in with_tempdir
    fn()
  File "/usr/local/lib/python3.11/site-packages/duplicity/dup_main.py", line 1612, in main
    do_backup(action)
  File "/usr/local/lib/python3.11/site-packages/duplicity/dup_main.py", line 1760, in do_backup
    incremental_backup(sig_chain, col_stats)
  File "/usr/local/lib/python3.11/site-packages/duplicity/dup_main.py", line 768, in incremental_backup
    bytes_written = write_multivol("inc", tarblock_iter, new_man_outfp, new_sig_outfp, config.backend)
                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/duplicity/dup_main.py", line 534, in write_multivol
    write_manifest_in_sequence(mf, man_outfp, command2vol_map)
  File "/usr/local/lib/python3.11/site-packages/duplicity/dup_main.py", line 402, in write_manifest_in_sequence
    info = command2vol_map[next(i)]

Will create a fix ASAP.