Update quay.io/coreos/etcd Docker tag to v3.5.18

| datasource | package             | from    | to      |
| ---------- | ------------------- | ------- | ------- |
| docker     | quay.io/coreos/etcd | v3.5.16 | v3.5.18 |


Signed-off-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

etcd-demo/docker-compose.yml

@@ -10,7 +10,7 @@ services:
       - "8080:8080"
   etcd:
     command: "-name etcd0 -advertise-client-urls http://${HOST_IP}:2379,http://${HOST_IP}:4001 -listen-client-urls http://0.0.0.0:2379,http://0.0.0.0:4001 -initial-advertise-peer-urls http://${HOST_IP}:2380 -listen-peer-urls http://0.0.0.0:2380 -initial-cluster-token etcd-cluster-1 -initial-cluster etcd0=http://${HOST_IP}:2380"
-    image: quay.io/coreos/etcd:v3.5.16
+    image: quay.io/coreos/etcd:v3.5.18
     container_name: etcd
     ports:
       - "4001:4001"