Add github actions yml files checker

Author: GuillaumeGomez

.github/workflows/ci.yml

@@ -27,6 +27,10 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
+      # We check that all github actions workflows have valid syntax
+      - name: Validate YAML file
+        run: yamllint .github/workflows/*
+
       - name: install `just`
         run: sudo snap install --edge --classic just