WIP: Add postgresql server to CI build

* `POSTGRES_PASSWORD` is required by the Docker image, but its value is not
important, because we can rely on the trust authentication setup for local
connections [1].
* 5432 is the default port and is expected by Rails.
* PostgreSQL v17 is currently the default version for Heroku [2].

[1]: https://hub.docker.com/_/postgres/#environment-variables
[2]: https://devcenter.heroku.com/articles/heroku-postgres-version-support#version-support

Author: floehopper

.github/workflows/build.yml

@@ -4,6 +4,17 @@ jobs:
   build:
     runs-on: ubuntu-latest
     timeout-minutes: 10
+    env:
+      PGHOST: localhost
+      PGUSER: postgres
+      PGPASSWORD: password
+    services:
+      postgres:
+        image: postgres:17
+        env:
+          POSTGRES_PASSWORD: password
+        ports:
+          - 5432:5432
     steps:
       - name: Checkout code
         uses: actions/checkout@v3