Unskip test that was skipped during nullable prototype work

It passes now; I'm guessing something was doing bad analysis at one
point and saying something was nullable when it wasn't.

Fixes dotnet#30035

src/EditorFeatures/CSharpTest/QuickInfo/SemanticQuickInfoSourceTests.cs

@@ -3728,8 +3728,7 @@ void M()
         }
 
         [WorkItem(543873, "http://vstfdevdiv:8080/DevDiv2/DevDiv/_workitems/edit/543873")]
-        [WorkItem(30035, "https://github.com/dotnet/roslyn/issues/30035")]
-        [Fact(Skip = "https://github.com/dotnet/roslyn/issues/30035"), Trait(Traits.Feature, Traits.Features.QuickInfo)]
+        [Fact, Trait(Traits.Feature, Traits.Features.QuickInfo)]
         public async Task TestNestedAnonymousType()
         {
             // verify nested anonymous types are listed in the same order for different properties