Experiment with a much shorter timeout.

tests/ImageSharp.Tests/Image/ImageTests.Decode_Cancellation.cs

@@ -95,7 +95,7 @@ public partial class ImageTests
             await Assert.ThrowsAnyAsync<OperationCanceledException>(async () =>
             {
                 using Image image = await Image.LoadAsync(options, "someFakeFile", cts.Token);
-            }).WaitAsync(TimeSpan.FromSeconds(30));
+            }).WaitAsync(TimeSpan.FromMilliseconds(600));
         }
     }
 }