Heroku, Rails 7 CI test pipeline, database errors

I'm trying to get Heroku Pipeline working with my Rails 7 application. Currently running into problems related to database connection / creation. In the pipeline test tab all tests fails and I get the following error:

Running 245 tests in parallel using 4 processes
We could not find your database: postgres. Which can be found in the database  configuration file located at config/database.yml.
To resolve this issue:
- Did you create the database for this app, or delete it? You may need to create   your database.
- Has the database name changed? Check your database.yml config has the correct   database name.
To create your database, run:
    bin/rails db:create
Couldn't create 'd7cd1vu5hke8mq-0' database. Please check your configuration.

[...]

DRb::DRbRemoteError: We could not find your database: postgres. Which can be found in the database configuration file located at config/database.yml.
To resolve this issue:
- Did you create the database for this app, or delete it? You may need to create your database.
- Has the database name changed? Check your database.yml config has the correct database name.
To create your database, run:
    bin/rails db:create
(ActiveRecord::NoDatabaseError)

I'm quite new to Heroku CI and Pipelines overall. My config/database.yml file looks like this:

default: &default
  adapter: postgresql
  encoding: unicode
  pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>
  username: postgres
  password: <%= ENV['WS_DATABASE_PASSWORD'] %>
  port: 5432

development:
  <<: *default
  database: db/development

# Warning: The database defined as "test" will be erased and
# re-generated from your development database when you run "rake".
# Do not set this db to the same as development or production.
test:
  <<: *default
  database: db/test

production:
  <<: *default
  database: db/production 

My production database works fine, but the errors occurs when running tests on Heroku.

I've also created a app.json file, but this didn't help either:

{
  "environments": {
    "test": {
      "addons":[
        "heroku-postgresql:mini",
        "heroku-redis:mini"
      ]
    }
  }
}

Any ideas on why my database connection and test suite won't run properly?

Remove user, password, and port settings in database.yml there is a solid doc explaining why here: Rails Database Connection Behavior

default: &default
  adapter: postgresql
  encoding: unicode
  pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>

And use heroku-postgresql:in-dyno addon for postgres tests in app.json as described here: Heroku CI In-Dyno Databases. You'll want the same for your Redis test env.

{
  "environments": {
    "test": {
      "addons":[
        "heroku-postgresql:in-dyno",
        "heroku-redis:in-dyno"
      ]
    }
  }
}