ci: pull database images from the ECR Public mirror

GitHub runners hit the Docker Hub pull rate limit for anonymous pulls
(toomanyrequests) on the Redis, PostgreSQL, and MySQL service containers.
The ECR Public mirror serves the same official images without that
limit.

Author: cardmagic

.github/workflows/ci.yml

@@ -66,7 +66,7 @@ jobs:
     timeout-minutes: 15
     services:
       redis:
-        image: redis:7
+        image: public.ecr.aws/docker/library/redis:7
         ports:
           - 6379:6379
         options: >-
@@ -87,7 +87,7 @@ jobs:
     timeout-minutes: 15
     services:
       postgres:
-        image: postgres:18
+        image: public.ecr.aws/docker/library/postgres:18
         env:
           POSTGRES_USER: solid_objects
           POSTGRES_PASSWORD: solid_objects
@@ -121,7 +121,7 @@ jobs:
         client: [ mysql2, trilogy ]
     services:
       mysql:
-        image: mysql:8.4
+        image: public.ecr.aws/docker/library/mysql:8.4
         env:
           MYSQL_USER: solid_objects
           MYSQL_PASSWORD: solid_objects