ci: Create separate `test` workflow that uses Postgres

.github/workflows/lint.yml

@@ -31,6 +31,3 @@ jobs:
 
       - name: Check code style
         run: mix credo
-
-      - name: Run tests
-        run: mix test

.github/workflows/test.yml

@@ -0,0 +1,44 @@
+# Create initial workflow based on GitHub's suggestion for Elixir.
+
+on:
+  push:
+    branches: ["main"]
+  pull_request:
+    branches: ["main"]
+
+jobs:
+  test:
+    name: Test codebase
+    runs-on: ubuntu-latest
+
+    services:
+      postgres:
+        image: postgres
+        options: >-
+          --health-cmd pg_isready
+          --health-interval 10s
+          --health-timeout 5s
+          --health-retries 5
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Set up Elixir
+        uses: erlef/setup-beam@v1
+        with:
+          elixir-version: '1.16.0'
+          otp-version: '26.0'
+
+      - name: Cache dependencies
+        uses: actions/cache@v3
+        with:
+          path: deps
+          key: ${{ runner.os }}-mix-${{ hashFiles('**/mix.lock') }}
+          restore-keys: ${{ runner.os }}-mix-
+
+      - name: Install dependencies
+        run: mix deps.get
+
+      - name: Run tests
+        run: mix test