chore: introduce the env vars

.github/workflows/REUSABLE_backend.yml

@@ -44,7 +44,7 @@ on:
         description: Versions of databases to test with. Should be array of strings encoded as JSON array
         type: string
         required: false
-        default: '["mysql:5.7", "mysql:8.0.30", "mysql:8.1.0", "mariadb"]'
+        default: '["mysql:5.7", "mysql:8.0.30", "mysql:8.1.0", "mariadb", "postgres:16"]'
 
       php_ini_values:
         description: PHP ini values
@@ -118,6 +118,14 @@ jobs:
         image: ${{ matrix.service }}
         ports:
           - 13306:3306
+      postgres:
+        image: ${{ matrix.service }}
+        ports:
+          - 13306:5432
+        env:
+          POSTGRES_USER: root
+          POSTGRES_PASSWORD: root
+          POSTGRES_DB: flarum_test
 
     name: 'PHP ${{ matrix.php }} / ${{ matrix.db }} ${{ matrix.prefixStr }}'