Add GRContext Metal backend test

Author: jeremy-visionaid

tests/SkiaSharp.Tests.Devices/Tests/iOS/iOSExtensionsTests.cs

@@ -1,5 +1,7 @@
-using CoreGraphics;
+using System;
+using CoreGraphics;
 using Foundation;
+using Metal;
 using Xunit;
 
 namespace SkiaSharp.Views.iOS.Tests
@@ -99,5 +101,21 @@ public void CGRectToSKRect(int x, int y, int w, int h)
 
 			Assert.Equal(expected, actual);
 		}
+
+		[SkippableFact]
+		public void GRContextDisposeDoesNotCrash()
+		{
+			var device = MTLDevice.SystemDefault!;
+			Skip.If(device == null, "Metal is not supported on this device.");
+
+			using var commandQueue = device.CreateCommandQueue();
+			using var backendContext = new GRMtlBackendContext()
+			{
+				Device = device,
+				Queue = commandQueue,
+			};
+
+			using var context = GRContext.CreateMetal(backendContext);
+		}
 	}
 }