Fix build in unrelated test code

tests/ImageSharp.Tests/Formats/WebP/WebpCommonUtilsTests.cs

@@ -106,7 +106,7 @@ public class WebpCommonUtilsTests
             174, 183, 189, 255,
             148, 158, 158, 255,
         };
-        Span<Bgra32> row = MemoryMarshal.Cast<byte, Bgra32>(rowBytes);
+        Span<Bgra32> row = MemoryMarshal.Cast<byte, Bgra32>((Span<byte>)rowBytes);
 
         bool noneOpaque;
         for (int length = 8; length < row.Length; length += 8)
@@ -188,7 +188,7 @@ public class WebpCommonUtilsTests
             174, 183, 189, 255,
             148, 158, 158, 255,
         };
-        Span<Bgra32> row = MemoryMarshal.Cast<byte, Bgra32>(rowBytes);
+        Span<Bgra32> row = MemoryMarshal.Cast<byte, Bgra32>((Span<byte>)rowBytes);
 
         bool noneOpaque;
         for (int length = 8; length < row.Length; length += 8)

tests/ImageSharp.Tests/Image/ImageFrameTests.cs

@@ -112,7 +112,7 @@ public class ImageFrameTests
             }
 
             byte[] expected = TestUtils.FillImageWithRandomBytes(image);
-            byte[] actual = new byte[expected.Length];
+            Span<byte> actual = new byte[expected.Length];
             if (byteSpan)
             {
                 image.Frames.RootFrame.CopyPixelDataTo(actual);

tests/ImageSharp.Tests/Image/ImageTests.cs

@@ -190,7 +190,7 @@ public partial class ImageTests
             }
 
             byte[] expected = TestUtils.FillImageWithRandomBytes(image);
-            byte[] actual = new byte[expected.Length];
+            Span<byte> actual = new byte[expected.Length];
             if (byteSpan)
             {
                 image.CopyPixelDataTo(actual);