streamingアプリの扱いはちょっと雑ですまん。こうして、
$ export HEROKU_APP=zundan-mastodon-streaming
$ heroku addons:detach HEROKU_POSTGRESQL_AMBER
$ heroku addons:detach DATABASE
$ heroku addons:attach postgresql-silhouetted-99516 --as DATABASE
こうじゃ
$ heroku addons
:
heroku-postgresql (postgresql-silhouetted-99516) standard-0 (billed to zundan-mastodon app) created
├─ as DATABASE
├─ as DATABASE on zundan-mastodon app
└─ as HEROKU_POSTGRESQL_ROSE on zundan-mastodon app