ci/cd: update GitHub Workflow

- use v4 of rlespinasse/github-slug-action (instead of v2.x)
  - the last "build-and-publish"-action threw a warning ("This version only support linux-based workflow, please use 'rlespinasse/github-slug-action@v3.x' instead")

.github/workflows/publish.yaml

@@ -20,7 +20,8 @@ jobs:
       with:
         username: ${{ github.repository_owner }}
         password: ${{ secrets.DOCKERHUB_PASSWORD }}
-    - uses: rlespinasse/github-slug-action@v2.x
+    - name: Inject slug/short variables
+      uses: rlespinasse/github-slug-action@v4
     - name: Build Docker image
       run: docker build --tag ${{ github.repository }}:${{ env.GITHUB_REF_SLUG }} .
     - name: Publish to DockerHub