Dispose of resized mask image when calculating diffs (#67)

ImageSharpCompare/ImageSharpCompare.cs

@@ -160,7 +160,7 @@
         /// <param name="pathExpectedImage"></param>
         /// <param name="resizeOption"></param>
         /// <returns>Mean and absolute pixel error</returns>
         public static ICompareResult CalcDiff(string pathActualImage, string pathExpectedImage, ResizeOption resizeOption = ResizeOption.DontResize)
         {
             using var actual = Image.Load(pathActualImage);
             using var expected = Image.Load(pathExpectedImage);
@@ -419,6 +419,7 @@
                 {
                     grown.Item1?.Dispose();
                     grown.Item2?.Dispose();
+                    grown.Item3?.Dispose();
                 }
             }