ci: bump actions/download-artifact from 6 to 7 (#458)

Bumps [actions/download-artifact](https://github.com/actions/download-artifact) from 6 to 7.
- [Release notes](https://github.com/actions/download-artifact/releases)
- [Commits](actions/download-artifact@v6...v7)

---
updated-dependencies:
- dependency-name: actions/download-artifact
  dependency-version: '7'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/interop.yml

@@ -124,20 +124,20 @@ jobs:
         run: sudo modprobe ip6table_filter
       - run: docker image ls
       - name: Download quic-network-simulator image
-        uses: actions/download-artifact@v6
+        uses: actions/download-artifact@v7
         with:
           name: images-quic-network-simulator
       - name: Download quic-interop-iperf-endpoint image
-        uses: actions/download-artifact@v6
+        uses: actions/download-artifact@v7
         with:
           name: images-quic-interop-iperf-endpoint
       - name: Download ${{ matrix.server }} Docker image
-        uses: actions/download-artifact@v6
+        uses: actions/download-artifact@v7
         with:
           name: image-${{ matrix.server }}
       - name: Download ${{ matrix.client }} Docker image
         if: ${{ matrix.server != matrix.client }}
-        uses: actions/download-artifact@v6
+        uses: actions/download-artifact@v7
         with:
           name: image-${{ matrix.client }}
       - name: Load docker images
@@ -203,7 +203,7 @@ jobs:
         with:
           python-version: 3.8
       - name: Download results
-        uses: actions/download-artifact@v6
+        uses: actions/download-artifact@v7
         with:
           pattern: results-*
       - name: Aggregate results