nettest: pass VERSION as an argument

This ensures that it is available when writing /app/version. Without
that, /app/version is empty and subctl show versions can't show the
corresponding version information.

Signed-off-by: Stephen Kitt <[email protected]>

Author: skitt

package/Dockerfile.nettest

@@ -1,6 +1,7 @@
 ARG FEDORA_VERSION=41
 
 FROM --platform=${BUILDPLATFORM} fedora:${FEDORA_VERSION} AS base
+ARG VERSION
 ARG FEDORA_VERSION
 ARG TARGETPLATFORM
 
@@ -12,6 +13,7 @@ RUN /dnf_install -a ${TARGETPLATFORM} -v ${FEDORA_VERSION} -r /output/nettest \
 
 FROM scratch
 ARG TARGETPLATFORM
+ARG VERSION
 ENV PATH="/app:$PATH"
 
 COPY --from=base /output/nettest /