Fixed unit tests.

Author: dlemstra

tests/Magick.NET.Tests/Formats/Bmp/BmpWriteDefinesTests/TheFormatProperty.cs

@@ -40,7 +40,10 @@ public void ShouldAllowBmpFormats(MagickFormat format)
         [InlineData((MagickFormat)int.MaxValue)]
         public void ShouldThrowExceptionWhenFormatIsInvalid(MagickFormat format)
         {
-            var defines = new BmpWriteDefines();
+            var defines = new BmpWriteDefines()
+            {
+                Format = MagickFormat.Bmp2,
+            };
 
             var exception = Assert.Throws<InvalidOperationException>(() => defines.Format = format);