[ci] wikigen: use diff for all branches and update for master

.gitlab-ci.yml

@@ -52,8 +52,9 @@ wikigen:
         SITE: [grenoble, lille, luxembourg, lyon, nancy, nantes, rennes, sophia, strasbourg, toulouse]
         DEBIAN_VERSION: [bookworm]
   script:
+    - if [ "$CI_COMMIT_BRANCH" = "master" ]; then export ACTION="update"; else export ACTION="diff"; fi
     - echo "$GRID5000_API" > "${HOME}/.grid5000_api.yml"
-    - bundle exec rake gen:wiki NAME=${GENERATOR} SITE=${SITE} DO=diff
+    - bundle exec rake gen:wiki NAME=${GENERATOR} SITE=${SITE} DO=${ACTION}
   only:
     refs:
       - master