Adds unit test for LoadAsync(Configuration configuration, string path).

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

@@ -49,6 +49,15 @@ namespace SixLabors.ImageSharp.Tests
                 }
             }
 
+            [Fact]
+            public async Task Path_Agnostic_Configuration_Async()
+            {
+                using (var img = await Image.LoadAsync(Configuration.Default, this.Path))
+                {
+                    VerifyDecodedImage(img);
+                }
+            }
+
             [Fact]
             public void Path_Decoder_Specific()
             {