build(deps): 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] <[email protected]>

Author: dependabot[bot]

.github/workflows/main.yml

@@ -49,23 +49,23 @@ jobs:
         python3 tests/runners/baseline_images.py -cevb _build
     - name: Upload test images on failure
       if: ${{ failure() }}
-      uses: actions/upload-artifact@v5
+      uses: actions/upload-artifact@v6
       with:
         name: images
         path: |
           _build/images
           _build/Baseline*tgz
     - name: Upload artifacts
       if: ${{ always() }}
-      uses: actions/upload-artifact@v5
+      uses: actions/upload-artifact@v6
       with:
         name: dist
         path: |
           dist/apidocs
           dist/built
     - name: Upload built website
       if: ${{ success() }}
-      uses: actions/upload-artifact@v5
+      uses: actions/upload-artifact@v6
       with:
         name: website
         path: |