ci: Fix container image repo name

The SSHCA container image is supposed to be published to the *packages*
organization, since it is an image for custom software, as opposed to a
customized OS.

ci/common.sh

@@ -5,7 +5,7 @@ escape_name() {
 }
 
 REGISTRY_URL=git.pyrocufflink.net
-NAMESPACE=containerimages
+NAMESPACE=packages
 NAME="${JOB_NAME#*/}"
 NAME=$(escape_name "${NAME%/*}")
 TAG=$(escape_name "${BRANCH_NAME}")