ci(backend): fix release container rules

.gitlab-ci/backend.yml

@@ -68,6 +68,5 @@ container:
     - IMAGE_TAG=`./.gitlab-ci/version.pl`
     - buildah bud -t ${IMAGE_TAG} --volume ${CI_PROJECT_DIR}/bin/:/tmp/uniworx-bin --file docker/fradrive/Dockerfile
     - buildah push --creds "${CI_REGISTRY_USER}:${CI_JOB_TOKEN}" ${IMAGE_TAG} ${CI_REGISTRY_IMAGE}/${IMAGE_TAG}
-  rules: # should be equivalent to *release-rules in .gitlab-ci.yml
-    - if: $CI_COMMIT_TAG =~ /^v[0-9\.]+$/
-    - if: $CI_COMMIT_TAG =~ /^v[0-9\.]+-test-.*$/
+  rules:
+    - if: ${PROD_BUILD} == -prod