[ci] Fix retrieval of CI_COMMIT_TAG env variable

bob/devtools/scripts/ci.py

@@ -71,7 +71,7 @@ def deploy(dry_run):
     from ..ci import is_stable
     stable = is_stable(package,
         os.environ['CI_COMMIT_REF_NAME'],
-        os.environ['CI_COMMIT_TAG'],
+        os.environ.get('CI_COMMIT_TAG'),
         os.environ['CI_PROJECT_DIR'])
 
     from ..constants import WEBDAV_PATHS