build(deps): bump actions/download-artifact from 4 to 6 (#628)

Bumps [actions/download-artifact](https://github.com/actions/download-artifact) from 4 to 6.
- [Release notes](https://github.com/actions/download-artifact/releases)
- [Commits](actions/download-artifact@v4...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]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/ci.yml

@@ -184,7 +184,7 @@ jobs:
   #       run: ls -R
 
   #     - name: Downloading artifacts
-  #       uses: actions/download-artifact@v4
+  #       uses: actions/download-artifact@v6
 
   #     - name: Display structure of downloaded artifact files
   #       run: ls -R
@@ -256,7 +256,7 @@ jobs:
           python-version: ${{ env.MAIN_PYTHON_VERSION }}
 
       # this downloads all artifacts
-      - uses: actions/download-artifact@v4
+      - uses: actions/download-artifact@v6
 
       - name: Display structure of downloaded files
         run: ls -R