Upgrade test database versions.

tests/end-to-end/docker-compose.yaml

@@ -1,17 +1,17 @@
 version: '3'
 services:
   postgresql:
-    image: postgres:11.6-alpine
+    image: postgres:12.2-alpine
     environment:
       POSTGRES_PASSWORD: test
       POSTGRES_DB: test
   mysql:
-    image: mariadb:10.4
+    image: mariadb:10.5
     environment:
       MYSQL_ROOT_PASSWORD: test
       MYSQL_DATABASE: test
   tests:
-    image: python:3.7-alpine3.10
+    image: python:3.8-alpine3.11
     volumes:
       - "../..:/app:ro"
     tmpfs: