ci: actually check formatting

.gitlab-ci.yml

 stages:
   - check
   - build
+  - deploy
 
 variables:
   GIT_SUBMODULE_STRATEGY: recursive
@@ -69,27 +70,14 @@ build-p6:
     paths: ['build/flow3r.elf']
     expire_in: 5 hours
 
-.pages: &pages
-  stage: build
+pages:
+  stage: deploy
+  only:
+    - main
   script:
     - cd docs
     - make html
     - mv _build/html ../public
-  rules:
-    - if: $CI_COMMIT_REF_NAME != $CI_DEFAULT_BRANCH
-
-preview pages:
-  <<: *pages
-  artifacts:
-    paths: ['public']
-    # shorter artifacts keep duration to be storage friendly
-    expire_in: 10m
-
-# only update public page for CI runs on protected default branch
-pages:
-  <<: *pages
-  rules:
-    - if: $CI_COMMIT_REF_NAME == $CI_DEFAULT_BRANCH
   artifacts:
     paths: ['public']
     expire_in: 1d