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](https://github.com/actions/upload-artifact/compare/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>

.github/workflows/ci.yml

@@ -299,7 +299,7 @@ jobs:
         if: github.event_name == 'push'
 
       - name: Upload archive
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: ${{ steps.archive-name.outputs.filename }}
           path: |
@@ -448,7 +448,7 @@ jobs:
           genhtml --output-directory=report --substitute "s#.*libloot#$(pwd)#g" --substitute 's#\\#/#g' merged.info
 
       - name: Upload report
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: Code coverage report
           path: report/