Screenshot tests aren't saving image dumps on CI

[AtkinsSJ]

On a recent CI run, we have

Fail: /home/runner/work/ladybird/ladybird/Tests/LibWeb/Screenshot/input/css-filter.html

but in the "Upload test artifacts" step, it reports no dumps:

No files were found with the provided path: /home/runner/work/ladybird/ladybird/Build/UI/test-dumps. No artifacts will be uploaded.

So either we're not saving screenshots like we should be, or we're looking in the wrong directory for them.

[AtkinsSJ]

Oh actually in the logs it does say they were dumped.

Dumped /home/runner/work/ladybird/ladybird/Build/UI/Headless/test-dumps/css-filter.png
Dumped /home/runner/work/ladybird/ladybird/Build/UI/Headless/test-dumps/css-filter-ref.png

So this is an issue with it saving/looking in different locations.