ci: run check-style first in check stage

.gitlab-ci.yml

 stages:
+  - check
   - test
   - build
   - deploy
@@ -33,7 +34,7 @@ build-openapi-scheme:
       - $OPENAPI_JSON
 
 check-style:
-  stage: test
+  stage: check
   image: python:3.11-slim
   before_script:
     # we do this, because YAML anchors are not supported when executing locally