Switch to building with Depot

Change-Id: I4547e671e11f76e6776192cc68040d5e2ff61be9
(cherry picked from commit 564caa8bd7f1cf771958a97b8fff7c9bef90e447)
diff --git a/images/nova/Dockerfile b/images/nova/Dockerfile
index c561040..2e687ac 100644
--- a/images/nova/Dockerfile
+++ b/images/nova/Dockerfile
@@ -1,10 +1,8 @@
-# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: © 2025 VEXXHOST, Inc.
+# SPDX-License-Identifier: GPL-3.0-or-later
 # Atmosphere-Rebuild-Time: 2024-12-17T01:27:44Z
 
-ARG REGISTRY
-ARG RELEASE
-
-FROM ${REGISTRY}/openstack-venv-builder:${RELEASE} AS build
+FROM openstack-venv-builder AS build
 ARG NOVA_GIT_REF=70a435fd519a0ebcc3ac9ad5254fefbf19c93e48
 ADD --keep-git-dir=true https://opendev.org/openstack/nova.git#${NOVA_GIT_REF} /src/nova
 RUN git -C /src/nova fetch --unshallow
@@ -24,7 +22,7 @@
     https://github.com/storpool/storpool-openstack-integration/raw/master/drivers/os_brick/openstack/antelope/storpool.py \
     /var/lib/openstack/lib/python3.10/site-packages/os_brick/initiator/connectors/storpool.py
 
-FROM ${REGISTRY}/openstack-python-runtime:${RELEASE}
+FROM openstack-python-runtime
 ADD https://github.com/novnc/noVNC.git#v1.4.0 /usr/share/novnc
 RUN <<EOF bash -xe
 apt-get update -qq