⬆️ 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/cache.yml

@@ -23,13 +23,13 @@ jobs:
           jb build lectures --path-output ./ --keep-going
           # TODO: Re-enable -W flag once all lectures are translated and warnings are resolved
       - name: Upload Execution Reports
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         if: failure()
         with:
           name: execution-reports
           path: _build/html/reports
       - name: Upload "_build" folder (cache)
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: build-cache
           path: _build

.github/workflows/ci.yml

@@ -60,7 +60,7 @@ jobs:
         run: |
           jb build lectures --path-output ./ -n --keep-going
       - name: Upload Execution Reports
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         if: failure()
         with:
           name: execution-reports