docker: specify registry to simplify Podman builds (#24607)

.devops/zendnn.Dockerfile

@@ -3,7 +3,7 @@ ARG BUILD_DATE=N/A
 ARG APP_VERSION=N/A
 ARG APP_REVISION=N/A
 
-FROM ubuntu:$UBUNTU_VERSION AS build
+FROM docker.io/ubuntu:$UBUNTU_VERSION AS build
 
 RUN apt-get update && \
     apt-get install -y gcc-13 g++-13 build-essential git cmake libssl-dev libomp-dev libnuma-dev python3 ca-certificates
@@ -30,7 +30,7 @@ RUN mkdir -p /app/full \
     && cp .devops/tools.sh /app/full/tools.sh
 
 ## Base image
-FROM ubuntu:$UBUNTU_VERSION AS base
+FROM docker.io/ubuntu:$UBUNTU_VERSION AS base
 
 ARG BUILD_DATE=N/A
 ARG APP_VERSION=N/A