Fix gitlab-ci variable

.gitlab-ci.yml

@@ -54,7 +54,7 @@ build_docs:
     - if test "$BRANCH_NAME" = 'main'; then beta=""; fi
     - RELEASE_DATE="$(date +'%Y/%m/%d')${beta}"
     - RELEASE_VERSION="$(date +'%Y')${beta}"
-    - make clean html SPHINXOPTS="-D version=${BUILD_VERSION} -D release=${RELEASE_DATE}"
+    - make clean html SPHINXOPTS="-D version=${RELEASE_VERSION} -D release=${RELEASE_DATE}"
   artifacts:
     paths:
       - docs/_build/html