Pin memcached image to 1.6.39-bookworm in docker-compose file

Author: ockham

docker-compose.yml

@@ -130,7 +130,10 @@ services:
   # The Memcached container.
   ##
   memcached:
-    image: memcached
+    # Pinning to the latest `bookworm` image is a temporary solution
+    # while the cause of recent failures can be investigated.
+    # See https://core.trac.wordpress.org/ticket/63876.
+    image: memcached:1.6.39-bookworm
 
     networks:
       - wpdevnet