ci: fix build cache (#950)

diff --git a/images/manila/Earthfile b/images/manila/Earthfile
index cd5dd98..0bdadbf 100644
--- a/images/manila/Earthfile
+++ b/images/manila/Earthfile
@@ -1,6 +1,5 @@
 VERSION 0.7
 
-ARG --global REGISTRY=ghcr.io/vexxhost/atmosphere
 ARG --global PROJECT=manila
 ARG --global RELEASE=2023.2
 ARG --global PROJECT_REF=98bc755673fe48a9c67203e4262315b048efe25d
@@ -16,6 +15,7 @@
   COPY +build/venv /var/lib/openstack
   DO ../+APT_INSTALL \
     --PACKAGES "iproute2 openvswitch-switch"
+  ARG REGISTRY=ghcr.io/vexxhost/atmosphere
   SAVE IMAGE --push \
     ${REGISTRY}/${PROJECT}:${RELEASE} \
     ${REGISTRY}/${PROJECT}:${PROJECT_REF}