Properly set sky_cover property of sky_material to Nil in setter

[ibotha]

issue 74259 seems to be caused by being the value being set to "RID()" in the setter for the sky_cover property. I was able to fix this by setting the sky cover property back to Variant::Nil when it is reset in the editor.

I have tested this locally by running the engine before the fix, seeing the bug is present, then running it after the fix and seeing it works as expected.

Bugsquad edit:

• Fixes ProceduralSkyMaterial doesn't update visually and stays completely white once a Cover Texture is added and removed #74259

[ibotha]

My understanding of the engine is limited. If it is meant to be the case that RID() behaves as a nil value then I can make that change too

[ibotha]

Noticed the formatting caused one of the tests to fail so I fixed it

[clayjohn]

Looks good! This pattern is used in a few other places in the codebase, so we will need to keep our eyes open to other areas where this might cause an issue

[clayjohn]

After looking into this a bit more, the same change is needed for PanoramaSkyMaterial and for PhysicalSkyMaterial. It would be nice to make those changes in this PR so they are all grouped together

[mhilbrunner]

See clayjohn's comment.

[ibotha]

Alright, I have updated the other sky materials, sorry it took a while for me to get back to this.

[clayjohn]

Looks great! The final step before merging is to squash all the commits together so that the whole PR only contains 1 big commit with all your changes. We like to merge one commit at a time to keep the git history clean and navigable.

If you don't know how to do that, we have a helpful tutorial in the official documentation https://docs.godotengine.org/en/latest/community/contributing/pr_workflow.html#the-interactive-rebase

[ibotha]

Looks great! The final step before merging is to squash all the commits together so that the whole PR only contains 1 big commit with all your changes. We like to merge one commit at a time to keep the git history clean and navigable.

If you don't know how to do that, we have a helpful tutorial in the official documentation https://docs.godotengine.org/en/latest/community/contributing/pr_workflow.html#the-interactive-rebase

Alright, The commit has been squashed

Changes done.

[akien-mga]

Thanks! And congrats for your first merged Godot contribution 🎉

[YuriSizov]

Cherry-picked for 4.0.4.