ci: fix build cache (#950)

diff --git a/images/ovn/Earthfile b/images/ovn/Earthfile
index 2ff4254..1fdcc2e 100644
--- a/images/ovn/Earthfile
+++ b/images/ovn/Earthfile
@@ -1,6 +1,5 @@
 VERSION 0.7
 
-ARG --global REGISTRY=ghcr.io/vexxhost/atmosphere
 ARG --global SERIES=23.03
 ARG --global VERSION=23.03.0-69
 
@@ -31,6 +30,7 @@
   ARG TARGETARCH
   ARG TARGETVARIANT
   COPY (+ovn-kubernetes/ovn-kube-util --GOARCH=$TARGETARCH --VARIANT=$TARGETVARIANT) /usr/bin
+  ARG REGISTRY=ghcr.io/vexxhost/atmosphere
   SAVE IMAGE --push \
     ${REGISTRY}/ovn-${NAME}:${SERIES} \
     ${REGISTRY}/ovn-${NAME}:${VERSION}