ci: update artifact actions to v4

Upgraded the artifact actions to version 4 and enabled the `merge-multiple` option to ensure better compatibility with our system.

Author: vinceAmstoutz

.github/workflows/docker.yaml

@@ -198,7 +198,7 @@ jobs:
       -
         name: Upload builder metadata
         if: fromJson(needs.prepare.outputs.push)
-        uses: actions/upload-artifact@v3
+        uses: actions/upload-artifact@v4
         with:
           name: metadata-builder-${{ matrix.variant }}
           path: /tmp/metadata/builder/*
@@ -207,7 +207,7 @@ jobs:
       -
         name: Upload runner metadata
         if: fromJson(needs.prepare.outputs.push)
-        uses: actions/upload-artifact@v3
+        uses: actions/upload-artifact@v4
         with:
           name: metadata-runner-${{ matrix.variant }}
           path: /tmp/metadata/runner/*
@@ -237,10 +237,11 @@ jobs:
     steps:
       -
         name: Download metadata
-        uses: actions/download-artifact@v3
+        uses: actions/download-artifact@v4
         with:
           name: metadata-${{ matrix.target }}-${{ matrix.variant }}
           path: /tmp/metadata
+          merge-multiple: true
       -
         name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v3