fix: Only sign and push to dockerhub if RELEASE_VERSION populated

mentioned in commit 4765c352

mentioned in commit 9cd65c64

mentioned in commit 3efacd62

mentioned in commit 60816128

mentioned in merge request hoppr/plugins/hoppr-openssf-scorecard-plugin!50 (closed)

mentioned in merge request hoppr-cop!310 (merged)

mentioned in merge request hoppr/plugins/hoppr-nexus-bundler!180 (merged)

mentioned in merge request hoppr/plugins/starter-plugin!10 (merged)