Fix WordPress 6.9-RC3 Docker image tag and source

The RC tags use the `beta-` prefix and aren't mirrored to ECR.

Changes:
- Use correct tag format `beta-6.9-RC3`
- Switch to Docker Hub since ECR doesn't mirror beta/RC tags

Author: oguzkocer

.buildkite/pipeline.yml

@@ -17,7 +17,7 @@ common_params:
     # - '6.4'
     # - '6.5'
     # - '6.6'
-    - '6.9-RC3'
+    - 'beta-6.9-RC3'
 
 steps:
   #

docker-compose.yml

@@ -4,7 +4,7 @@ services:
             context: .
             dockerfile: wordpress.Dockerfile
             args:
-                WORDPRESS_VERSION: ${WORDPRESS_VERSION:-6.9-RC3}
+                WORDPRESS_VERSION: ${WORDPRESS_VERSION:-beta-6.9-RC3}
         container_name: 'wordpress'
         ports:
             - '80:80'

wordpress.Dockerfile

@@ -1,6 +1,7 @@
-ARG WORDPRESS_VERSION="6.9-RC3"
+ARG WORDPRESS_VERSION="beta-6.9-RC3"
 
-FROM public.ecr.aws/docker/library/wordpress:${WORDPRESS_VERSION}
+# Using Docker Hub directly since ECR doesn't mirror beta/RC tags
+FROM docker.io/library/wordpress:${WORDPRESS_VERSION}
 
 RUN apt-get update  \
   && apt-get install -y wget gpg