Use new environment variable names from CI

gitlab/before_build.sh

@@ -37,7 +37,7 @@ fi
 
 # When building a tag, do not use beta wheels
 PIPOPTS="${PIPOPTS} --use-wheel --no-index"
-if [ -z "${CI_BUILD_TAG}" ]; then
+if [ -z "${CI_COMMIT_TAG}" ]; then
   PIPOPTS="${PIPOPTS} --pre"
 fi