Fixed flipy issue

[ebogo1]

Fixes #8852. Merge after release.

@ptrgags

[cesium-concierge]

Thank you so much for the pull request @ebogo1! I noticed this is your first pull request and I wanted to say welcome to the Cesium community!

The Pull Request Guidelines is a handy reference for making sure your PR gets accepted quickly, so make sure to skim that.

• ❌ Missing CONTRIBUTORS.md entry.
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[lilleyse]

@ebogo1 I added you to the Cesium GS CLA

[lilleyse]

Here's a Sandcastle for testing: http://localhost:8080/Apps/Sandcastle/index.html#c=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

[ptrgags]

I tried the sandcastle myself, I confirmed that it's a black rectangle on master, and a gradient on this branch.

[ptrgags]

@lilleyse let me know it's safe to merge this now. I checked it over one last time, everything looks good.

Thanks @ebogo1!