Upgrade CI to Docker 20.10.15

Closes gh-30988

ci/images/get-docker-url.sh

@@ -1,5 +1,5 @@
 #!/bin/bash
 set -e
 
-version="20.10.14"
+version="20.10.15"
 echo "https://download.docker.com/linux/static/stable/x86_64/docker-$version.tgz";