Release workflow

This PR adds a release workflow that build an artefact with
dune-release.

The workflow runs only on branch `v*.*.x`.

Should be tested on the branch `v2.5.x`.

.github/workflows/release.yml

@@ -0,0 +1,39 @@
+name: Release
+
+on:
+  pull_request:
+    branches:
+      - 'v*.*.x'
+
+env:
+  OPAMYES: true
+
+jobs:
+  dune_release:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+        with:
+          persist-credentials: false
+
+      - name: Use OCaml 5.0.0
+        uses: ocaml/setup-ocaml@v2
+        with:
+          ocaml-compiler: 5.0.0
+          dune-cache: true
+
+      - name: Install dependencies
+        run: opam exec -- make deps
+
+      - name: Install dune-release
+        run: opam install dune-release
+
+      - name: Build the distribution archive
+        run: opam exec -- dune-release distrib
+
+      - name: Upload the artefact
+        uses: actions/upload-artifact@v3
+        with:
+          name: distribution archive
+          path: _build/alt-ergo-*.tbz