fix(ci): recreate doc environment from scratch

do not reuse artifact. They have different conditions, and lint_doc artifact
    should be kept to see the MR doc related results.

closes #206

.gitlab-ci.yml

@@ -205,7 +205,7 @@ pages:
   before_script:
     - pip install tox
   script:
-    - tox -e doc
+    - tox -re doc
     - mv .tox/doc/tmp/html public
   artifacts:
     paths: