Skip WebGPU drawing tests on Linux

Author: JimBobSquarePants

tests/ImageSharp.Drawing.Tests/Processing/Backends/WebGPUDrawingBackendTests.cs

@@ -1,6 +1,9 @@
 // Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
 
+#if !OS_Linux
+// WebGPU is failing in our CI environment in Ubuntu with
+// WebGPU adapter request failed with status 'Unavailable'
 using SixLabors.Fonts;
 using SixLabors.ImageSharp.Drawing.Processing;
 using SixLabors.ImageSharp.Drawing.Processing.Backends;
@@ -970,3 +973,4 @@ private static Buffer2DRegion<TPixel> GetFrameRegion<TPixel>(Image<TPixel> image
         where TPixel : unmanaged, IPixel<TPixel>
         => new(image.Frames.RootFrame.PixelBuffer, image.Bounds);
 }
+#endif