check if the formatting is valid

Author: efcasado

.github/workflows/samples-elixir.yaml

@@ -34,6 +34,9 @@ jobs:
       - name: mix deps.get
         run: mix deps.get
         working-directory: ${{ matrix.sample }}
+      - name: mix test
+        run: mix format --check-formatted
+        working-directory: ${{ matrix.sample }}
       - name: mix test
         run: mix test
         working-directory: ${{ matrix.sample }}