[DRE-maint] Bug#1015302: Upgrading 14.10.5 to 15.0.4 aborts on db:migrate

[Maximilian Stein]

Hi Patrick,

Your issue seems to be the same as Bug#1015301 that I just filed earlier 
today.

I actually shared a workaround that allowed me to finish the upgrade by 
temporarily marking the failed background migrations as successful in 
the database. Maybe you wanna have a look there: 
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1015301.

Best,
Maximilian