ci: only render on main

Refs #3

.gitlab-ci.yml

@@ -21,6 +21,8 @@ before_script:
 
 pages:
   stage: deploy
+  only:
+    - main
   script:
     - R -q -e 'rmarkdown::render("Formation_airGRiwrm.Rmd", "xaringan::moon_reader", output_file = "index.html")'
     - mkdir public