⬆️ Bump actions/upload-artifact from 5 to 6 (#352)

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>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Matt McKay <mmcky@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/ci.yml

@@ -56,14 +56,14 @@ jobs:
         env:
           SITE_PATH: lecture-python-programming.myst/_build/html
       - name: Upload Playwright Report
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         if: always()
         with:
           name: playwright-report
           path: playwright-report/
           retention-days: 30
       - name: Upload Test Results (on failure)
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         if: steps.visual-tests.outcome == 'failure'
         with:
           name: visual-test-diff