Fix syntax and also set build arg

.woodpecker/.base-os.yml

@@ -20,6 +20,8 @@ steps:
     image: woodpeckerci/plugin-docker-buildx
     settings:
       repo: gitea.simcop2387.info/simcop2387/perl-os-base
+      build_args:
+        VERSION: ${DEBIAN_VERSION}
       dockerfile: os-base/Dockerfile 
       auto_tag: false
       tags: 

os-base/Dockerfile

@@ -1,5 +1,5 @@
 ARG VERSION
-FROM debian:$VERSION-backports
+FROM debian:$VERSION
 LABEL maintainer="Ryan Voots <simcop@cpan.org>"
 
 ENV DEBIAN_FRONTEND=noninteractive
@@ -27,7 +27,7 @@ RUN perl -i.bak -pE '$x=$_; $x=~s|^deb |deb-src |g;$_.=$x' /etc/apt/sources.list
        patch \
        procps \
        zlib1g-dev \
-       xz-utils
+       xz-utils \
     && apt-get purge -y --auto-remove -o APT::AutoRemove::RecommendsImportant=false \
     && rm -fr /var/cache/apt/* /var/lib/apt/lists/*