Generate website preview link even if build fails on PRs

Could add `continue-on-error: true` Here https://github.com/xarray-contrib/xarray-tutorial/blob/321706a311dfae6f3d3532c8892a7b469a074f0e/.github/workflows/preview.yaml#L34 

Currently the preview link is skipped even if there are just warnings (https://github.com/xarray-contrib/xarray-tutorial/actions/runs/8013509881)