Merge pull request #6058 from Goober5000/skybox_orientation_and_alpha #602

Job	Run time
Linux (Debug, gcc-9)	13m 46s
Linux (Debug, gcc-13)	12m 10s
Linux (Debug, clang-16)	13m 13s
Linux (Release, gcc-9)	10m 15s
Linux (Release, gcc-13)	10m 36s
Linux (Release, clang-16)	12m 34s
Linux (Debug, gcc-13, -DFSO_BUILD_WITH_OPENGL=OFF -DFSO_BUILD_WITH_VULKAN=OFF)	11m 19s
Linux (Release, gcc-13, -DFSO_BUILD_WITH_OPENGL=OFF -DFSO_BUILD_WITH_VULKAN=OFF)	10m 26s
	1h 34m 19s

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