I saw this go by in the logs, but the upgrade continued with apparent success:
Waiting for Unicorn to reload...........................................................
$ bundle exec rake assets:flush_sw
rake aborted!
Don't know how to build task 'assets:flush_sw' (See the list of available tasks with `rake --tasks`)
Did you mean? assets:clean
/var/www/discourse/vendor/bundle/ruby/2.6.0/gems/rake-13.0.1/exe/rake:27:in `<top (required)>'
/usr/local/bin/bundle:23:in `load'
/usr/local/bin/bundle:23:in `<main>'
(See full trace by running task with --trace)
WARNING: Unable to flush service worker file
Running post deploy migrations
This won’t cause any issues updating, just noise in the logs which you can ignore for now - flush_sw is a new rake task that will exist once we re-add it. I’ve been working out some issues with the rake task in a draft PR, but for now those errors in the logs are harmless.