ci(earthly): Push multiarch builds

.gitlab-ci.yml

@@ -16,4 +16,4 @@ build:
       else
         export BUILD_ARGS="${BUILD_ARGS} --tag=$CI_COMMIT_REF_SLUG --latest=false"
       fi
-    - earthly --ci --allow-privileged --push ${ARGS} --platform=linux/amd64 --platform=linux/arm64 +container --registry=${CI_REGISTRY_IMAGE} ${BUILD_ARGS}
+    - earthly --ci --allow-privileged --push ${ARGS} +multiarch-container --registry=${CI_REGISTRY_IMAGE} ${BUILD_ARGS}

Earthfile

@@ -37,3 +37,6 @@ container:
         LABEL "quay.expires-after"="12w"
     END
     SAVE IMAGE --push ${registry}:${tag}
+
+multiarch-container:
+    BUILD --platform=linux/amd64 --platform=linux/arm64 +container