check access before clearing job queue.

tests/Avalonia.RenderTests/TestBase.cs

@@ -285,7 +285,10 @@ namespace Avalonia.Direct2D1.RenderTests
 
         public void Dispose()
         {
-            Dispatcher.UIThread.RunJobs();
+            if (Dispatcher.UIThread.CheckAccess())
+            {
+                Dispatcher.UIThread.RunJobs();
+            }
         }
     }
 }

tests/Avalonia.UnitTests/TestWithServicesBase.cs

@@ -18,7 +18,11 @@ namespace Avalonia.UnitTests
 
         public void Dispose()
         {
-            Dispatcher.UIThread.RunJobs();
+            if (Dispatcher.UIThread.CheckAccess())
+            {
+                Dispatcher.UIThread.RunJobs();
+            }
+            
             _scope.Dispose();
         }
     }

tests/Avalonia.UnitTests/UnitTestApplication.cs

@@ -46,7 +46,11 @@ namespace Avalonia.UnitTests
             Dispatcher.UIThread.UpdateServices();
             return Disposable.Create(() =>
             {
-                Dispatcher.UIThread.RunJobs();
+                if (Dispatcher.UIThread.CheckAccess())
+                {
+                    Dispatcher.UIThread.RunJobs();
+                }
+
                 scope.Dispose();
                 Dispatcher.UIThread.UpdateServices();
             });