Make Changelog available in publish job

The changelog isn't an artifact but in the repository itself. So in
addition to downloading the build artifacts the repository must also be
checked out.

Author: ServiusHack

.github/workflows/release.yml

@@ -41,6 +41,9 @@ jobs:
     needs: build
 
     steps:
+    - name: Checkout
+      uses: actions/checkout@v4
+
     - uses: actions/download-artifact@v4
       with:
         merge-multiple: true