The error was farther up in the build log:
…
docker_manager is already at latest compatible version
wp-discourse is already at latest compatible version
I, [2023-11-10T21:08:17.388213 #1] INFO -- : > cd /var/www/discourse && su discourse -c 'bundle exec rake db:migrate'
Plugin name is 'discourse-topic-voting', but plugin directory is named 'discourse-voting'
rake aborted!
ActiveRecord::StatementInvalid: PG::InsufficientPrivilege: ERROR: permission denied for table users (ActiveRecord::StatementInvalid)
So good news! It’s connecting fine, it’s that DB permissions need adjusting.