Added Redis via Docker

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Redis can be utilised for various caching purposes within Ghost. This PR adds
a Redis service to the docker-compose file to allow for easier local development
when Redis is required.

.github/scripts/docker-compose.yml

@@ -21,3 +21,9 @@ services:
       test: "mysql -uroot -proot ghost -e 'select 1'"
       interval: 1s
       retries: 120
+  redis:
+    image: redis:7.2
+    container_name: ghost-redis
+    ports:
+      - "6379:6379"
+    restart: always