wip: ensure TAG is always set on docker build

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

Author: mefellows

script/release-workflow/docker-build.sh

@@ -9,7 +9,7 @@ DOCKER_IMAGE_ORG_AND_NAME="${DOCKER_REPOSITORY:-pactfoundation}/pact-broker"
 for arch in $ARCHES; do 
     docker buildx build \
     --platform linux/$arch \
-    --build-arg VERSION=${TAG} \
+    --build-arg VERSION="${TAG:-dev}" \
     --output type=docker \
     --tag ${DOCKER_IMAGE_ORG_AND_NAME}:latest-${arch} \
     .