Drop mysql2 support, settle on postgresql

It's enough work to support one database, let's settle on
the defacto Rails default.

.github/workflows/next-rails.yml

@@ -12,6 +12,7 @@ jobs:
     runs-on: ubuntu-latest
     name: next-rails
     env:
+      OSEM_DB_HOST: localhost
       RAILS_ENV: test
     strategy:
       matrix:
@@ -29,7 +30,6 @@ jobs:
           bundler-cache: true
       - name: Prepare spec
         run: |
-          rm -f osem_test osem_development
           bundle exec rake db:setup --trace
           bundle exec bin/rails webdrivers:chromedriver:update
       - name: spec/${{ matrix.suite }}
@@ -40,3 +40,15 @@ jobs:
         with:
           project-token: ${{ secrets.CODACY_PROJECT_TOKEN }}
           coverage-reports: coverage/coverage.xml
+    services:
+      postgres:
+        image: postgres:16-alpine
+        env:
+          POSTGRES_PASSWORD: mysecretpassword
+        options: >-
+          --health-cmd pg_isready
+          --health-interval 10s
+          --health-timeout 5s
+          --health-retries 5
+        ports:
+          - 5432:5432