Fix source generator exceptions appearing when use "@+internal keyword" as type or namespace name in C# script

modules/mono/editor/Godot.NET.Sdk/Godot.SourceGenerators.Tests/TestData/Sources/KeywordClassNameAndNamespace.cs

@@ -0,0 +1,8 @@
+using Godot;
+
+namespace @namespace
+{
+    partial class @class : GodotObject
+    {
+    }
+}