Fix ktxTexture2_DecodeAstc documentation. #1005

Job	Run time
windows (windows-latest, Visual Studio 17 2022, v143, x64, NO, Debug,Release, ON, ON, OpenGL+Vulk...	25m 57s
windows (windows-latest, Visual Studio 17 2022, v143, x64, NO, Release, OFF, OFF, OFF, OFF, OFF, ...	3m 43s
windows (windows-latest, Visual Studio 17 2022, v143, x64, NO, Release, OFF, OFF, OFF, OFF, OFF, ...	3m 57s
windows (windows-latest, Visual Studio 17 2022, v143, x64, NO, Release, OFF, OFF, OFF, OFF, OFF, ...	4m 13s
windows (windows-latest, Visual Studio 17 2022, CLangCL, x64, NO, Debug,Release, ON, ON, OpenGL+V...	26m 34s
windows (windows-latest, Visual Studio 17 2022, CLangCL, x64, NO, Release, OFF, OFF, OFF, OFF, OF...	4m 36s
windows (windows-latest, Visual Studio 17 2022, CLangCL, x64, NO, Release, OFF, OFF, OFF, OFF, OF...	4m 29s
windows (windows-latest, Visual Studio 17 2022, CLangCL, x64, NO, Release, OFF, OFF, OFF, OFF, OF...	6m 57s
windows (windows-2019, Visual Studio 16 2019, v142, x64, Debug,Release, ON, ON, OpenGL+Vulkan, ON...	24m 44s
windows (windows-latest, Visual Studio 17 2022, CLangCL, arm64, Debug,Release, ON, ON, OpenGL+Vul...	18m 34s
	2h 3m 44s

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