Migrate sync workflow to actions/[upload-download] to v4

See https://github.com/actions/upload-artifact/blob/main/docs/MIGRATION.md#multiple-uploads-to-the-same-named-artifact

Author: umbynos

.github/workflows/sync-labels.yml

@@ -71,13 +71,13 @@ jobs:
           file-url: https://raw.githubusercontent.com/arduino/tooling-project-assets/main/workflow-templates/assets/sync-labels/${{ matrix.filename }}
 
       - name: Pass configuration files to next job via workflow artifact
-        uses: actions/upload-artifact@v3
+        uses: actions/upload-artifact@v4
         with:
           path: |
             *.yaml
             *.yml
           if-no-files-found: error
-          name: ${{ env.CONFIGURATIONS_ARTIFACT }}
+          name: ${{ env.CONFIGURATIONS_ARTIFACT }}-${{ matrix.filename }}
 
   sync:
     needs: download
@@ -109,10 +109,11 @@ jobs:
         uses: actions/checkout@v4
 
       - name: Download configuration files artifact
-        uses: actions/download-artifact@v3
+        uses: actions/download-artifact@v4
         with:
-          name: ${{ env.CONFIGURATIONS_ARTIFACT }}
+          pattern: ${{ env.CONFIGURATIONS_ARTIFACT }}-* # Download all configuration files
           path: ${{ env.CONFIGURATIONS_FOLDER }}
+          merge-multiple: true
 
       - name: Remove unneeded artifact
         uses: geekyeggo/delete-artifact@v5