Bump actions/download-artifact from 5 to 6

Bumps [actions/download-artifact](https://github.com/actions/download-artifact) from 5 to 6.
- [Release notes](https://github.com/actions/download-artifact/releases)
- [Commits](actions/download-artifact@v5...v6)

---
updated-dependencies:
- dependency-name: actions/download-artifact
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

.github/workflows/ci.yml

@@ -123,7 +123,7 @@ jobs:
     needs: [ build ]
     steps:
       - uses: actions/checkout@v5
-      - uses: actions/download-artifact@v5
+      - uses: actions/download-artifact@v6
         if: ${{ matrix.distro != 'docker' }}
         with:
           name: debian-${{ matrix.distro }}
@@ -209,17 +209,17 @@ jobs:
       - uses: actions/checkout@v5
 
       - name: Download 20.04 debian artifact
-        uses: actions/download-artifact@v5
+        uses: actions/download-artifact@v6
         with:
           name: debian-focal
 
       - name: Download 22.04 debian artifact
-        uses: actions/download-artifact@v5
+        uses: actions/download-artifact@v6
         with:
           name: debian-jammy
 
       - name: Download 24.04 debian artifact
-        uses: actions/download-artifact@v5
+        uses: actions/download-artifact@v6
         with:
           name: debian-noble