[fix] add default PG db as per https://github.com/odoo/odoo/issues/27447#issuecomment-427840100

templates/prod.yaml.j2

@@ -50,6 +50,7 @@ services:
         image: postgres:{{ odoo_db_version }}-alpine
         container_name: odoo_db
         environment:
+            POSTGRES_DB: "postgres"
             POSTGRES_USER: "{{ odoo_prod.db_user }}"
             POSTGRES_PASSWORD: "{{ odoo_prod.db_pass }}"
         labels:

templates/test.yaml.j2

@@ -51,6 +51,7 @@ services:
         image: postgres:{{ odoo_db_version }}-alpine
         container_name: {{ item.dir }}_db
         environment:
+            POSTGRES_DB: "postgres"
             POSTGRES_USER: "{{ item.db_user }}"
             POSTGRES_PASSWORD: "{{ item.db_pass }}"
         labels: