In Rails 6 due to internal changes, the following sequence no longer works:
```
RAILS_ENV=test bin/rake db:migrate
RAILS_ENV=test bin/rake db:schema:dump
dropdb discourse_test
createdb discourse_test
RAILS_ENV=test bin/rake db:schema:load
RAILS_ENV=test bin/rake db:migrate
```
What appears to be happening is that our tracking of plugin migrations is
being missed on schema:dump or load.
A more comprehensive fix restoring schema:dump / load support will be
investigated.