ci: fix warm-proxy variable expansion (use $VAR not ${VAR} for shell vars)

.drone.yml

@@ -76,10 +76,9 @@ steps:
     image: golang:1.26
     commands:
       - MODULE=$(go list -m)
-      - VERSION=${DRONE_TAG}
-      - echo "Warming proxy for $MODULE@$VERSION"
-      - curl -sf "https://git.beatrice.wtf/api/packages/panic.haus/go/${MODULE}/@v/${VERSION}.info"
-      - echo "Registered $MODULE@$VERSION in Gitea package registry"
+      - echo "Warming proxy for $MODULE@${DRONE_TAG}"
+      - curl -sf "https://git.beatrice.wtf/api/packages/panic.haus/go/$MODULE/@v/${DRONE_TAG}.info"
+      - echo "Registered $MODULE@${DRONE_TAG} in Gitea package registry"
 
 volumes:
   - name: go-mod-cache