Fix Docker version error in Redis GHA

The previous version of the local action failed due to:

```
Error response from daemon: client version 1.40 is too old. Minimum supported API version is 1.44, please upgrade your client to a newer version
```

so this commit upgrades the `docker` base image version. While we're at
it, also update the `redis` base image version we use inside the
`docker` docker container.

Author: chris-janidlo

.github/actions/redis/Dockerfile

@@ -1,4 +1,4 @@
-FROM docker:stable
+FROM docker:latest
 RUN apk add --update bash
 COPY run-redis.sh /run-redis.sh
 ENTRYPOINT ["/run-redis.sh"]

.github/actions/redis/action.yml

@@ -8,7 +8,7 @@ inputs:
   redis-version:
     description: 'The version of Redis to use'
     required: false
-    default: '6.2.5'
+    default: '8.6.0'
 
 runs:
   using: 'docker'