Bump actions/upload-artifact from 5 to 6

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

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

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

Author: dependabot[bot]

.github/workflows/linkcheck.yml

@@ -29,7 +29,7 @@ jobs:
       run: |
         $SPHINX -d _doctrees/ doc/ _build/linkcheck/ -b linkcheck -q
     - name: Upload results
-      uses: actions/upload-artifact@v5
+      uses: actions/upload-artifact@v7
       if: ${{ success() || failure() }}
       with:
         name: linkcheck

.github/workflows/publish.yml

@@ -14,7 +14,7 @@ jobs:
       run: |
         uv run --locked --with build python -m build
     - name: Store the distribution packages
-      uses: actions/upload-artifact@v5
+      uses: actions/upload-artifact@v7
       with:
         name: dist
         path: dist