ci(deps): bump actions/download-artifact from 5.0.0 to 6.0.0

Bumps [actions/download-artifact](https://github.com/actions/download-artifact) from 5.0.0 to 6.0.0.
- [Release notes](https://github.com/actions/download-artifact/releases)
- [Commits](https://github.com/actions/download-artifact/compare/v5.0.0...v6.0.0)

---
updated-dependencies:
- dependency-name: actions/download-artifact
  dependency-version: 6.0.0
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

.github/workflows/python-distributions.yml

@@ -159,7 +159,7 @@ jobs:
           # See https://github.com/pypa/twine/issues/1216
           pip install "twine>=6.1.0" "packaging>=24.2"
       - name: Download sdist
-        uses: actions/download-artifact@v5.0.0
+        uses: actions/download-artifact@v6.0.0
         with:
           name: artifact-source
           path: dist
@@ -183,7 +183,7 @@ jobs:
       url: https://pypi.org/p/dulwich
     steps:
       - name: Download distributions
-        uses: actions/download-artifact@v5.0.0
+        uses: actions/download-artifact@v6.0.0
         with:
           merge-multiple: true
           pattern: artifact-*