Add a dune package management GHA workflow (ocaml-ppx#2696)

This introduces a workflow for dune package management. It would help us ensure the package builds with dune developer preview

Author: Sudha247

.github/workflows/build-dune.yml

@@ -0,0 +1,18 @@
+name: Build on Dune PM
+
+on: [push, pull_request]
+
+jobs:
+  build:
+    strategy:
+      matrix:
+        runs-on: [ ubuntu-latest, macos-latest ]
+    runs-on: ${{ matrix.runs-on }}
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+      - name: Use dune
+        uses: ocaml-dune/setup-dune@v0.0.1
+        with:
+          automagic: true