[monotouch-test] Ignore the MetalPerformanceShadersGraph.MnistTest test, it fails randomly. (#20033)

tests/monotouch-test/MetalPerformanceShaders/MnistTest.cs

@@ -53,6 +53,7 @@ namespace MonoTouchFixtures.MetalPerformanceShadersGraph {
 		}
 
 		[Test]
+		[Ignore ("This test frequently fails, so just ignore it for now.")]
 		public void Run ()
 		{
 			using (var tester = new MnistTest ()) {