Bump actions/download-artifact from 4 to 6

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]>

Author: dependabot[bot]

.github/workflows/pythonapp.yml

@@ -58,7 +58,7 @@ jobs:
         python -m pip install --upgrade pip
         pip install -U setuptools setuptools_scm
         pip install "pytest<9"
-    - uses: actions/download-artifact@v4
+    - uses: actions/download-artifact@v6
       with:
         name: dist
         path: dist
@@ -75,7 +75,7 @@ jobs:
     - uses: actions/setup-python@v5
       with:
         python-version: "3.10"
-    - uses: actions/download-artifact@v4
+    - uses: actions/download-artifact@v6
       with:
         name: dist
         path: dist
@@ -87,7 +87,7 @@ jobs:
     if: github.event_name == 'push' && startsWith(github.event.ref, 'refs/tags')
     needs: [dist_check, test]
     steps:
-    - uses: actions/download-artifact@v4
+    - uses: actions/download-artifact@v6
       with:
         name: dist
         path: dist