UX update for list of failed tests

The line "The following tests failed: " was appearing when there were
no test failures. This update simply updates it to only display when
there are failed tests.

Turkey/TestOutputFormat.cs

@@ -63,11 +63,14 @@ public async override Task AfterRunningTestAsync(string name, TestResult result,
 
             public async override Task PrintFailedTests()
             {
-                Console.WriteLine();
-                Console.WriteLine("The following tests failed: ");
-                foreach(var test in failedTests)
+                if (failedTests.Count != 0)
                 {
-                   Console.WriteLine($"{string.Format("{0,-30}", test.Name)}({test.Duration})");
+                    Console.WriteLine();
+                    Console.WriteLine("The following tests failed: ");
+                    foreach(var test in failedTests)
+                    {
+                        Console.WriteLine($"{string.Format("{0,-30}", test.Name)}({test.Duration})");
+                    }
                 }
             }