disable flaky test

src/Workspaces/CoreTest/SolutionTests/SolutionTests.cs

@@ -923,7 +923,7 @@ private ObjectReference<SourceText> GetObservedTextAsync(Solution solution, Docu
         }
 
         [MethodImpl(MethodImplOptions.NoInlining)]
-        [Fact, Trait(Traits.Feature, Traits.Features.Workspace)]
+        [Fact(Skip = "https://github.com/dotnet/roslyn/issues/13433"), Trait(Traits.Feature, Traits.Features.Workspace)]
         public void TestGetSyntaxRootDoesNotKeepRootAlive()
         {
             var pid = ProjectId.CreateNewId();