database backup through bbr feature fails randomly with concourse 7.2

[JCL38-ORANGE]

Bug Report

• Concourse version: 7.2.0
• Deployment type (BOSH/Docker/binary): BOSH
• Infrastructure/IaaS: Openstack and vSphere
• It was working everytime with concourse 6

We have a backup configured with BBR (Bosh Backup Restore).
Randomly it fails with the message :
pg_dump: [archiver (db)] query failed: ERROR: relation "public.build_event_id_seq_15739788" does not exist
LINE 1: SELECT last_value, is_called FROM public.build_event_id_seq_...
^
pg_dump: [archiver (db)] query was: SELECT last_value, is_called FROM public.build_event_id_seq_15739788
2021/06/08 02:15:19 You may need to delete the artifact-file that was created before re-running.

[alexnguyen91]

While #145 provide the retry feature, unfortunately it's broken because 'set -e' and '((ticks++))' don't work well together
#157 should fix the retry process. Until it get merged, you could modify the backup script to be the same with that PR #