Add turtle for testing

http://css3.bradshawenterprises.com/filters/

Former-commit-id: 65f2931f38d1b159291a39178ac743d628477483
Former-commit-id: 1cb0efb5f0c944a6f0aed5b191ae692b35f36b0f
Former-commit-id: 71c2bbee979c71225b669ae0226c491f23996ede

tests/ImageProcessorCore.Tests/FileTestBase.cs

@@ -21,6 +21,7 @@ namespace ImageProcessorCore.Tests
         {
             //"TestImages/Formats/Jpg/Floorplan.jpeg", // Perf: Enable for local testing only
             "TestImages/Formats/Jpg/Calliphora.jpg",
+            "TestImages/Formats/Jpg/turtle.jpg",
             //"TestImages/Formats/Jpg/fb.jpg", // Perf: Enable for local testing only
             //"TestImages/Formats/Jpg/progress.jpg", // Perf: Enable for local testing only
             //"TestImages/Formats/Jpg/gamma_dalai_lama_gray.jpg", // Perf: Enable for local testing only