correctly annotate nullable in generated sources

Author: dealloc

src/Helldivers-2-SourceGen/Parsers/PlanetRegionsParser.cs

@@ -12,7 +12,7 @@ public class PlanetRegionsParser : BaseJsonParser
     /// <inheritdoc />
     protected override (string Type, string Source) Parse(string json)
     {
-        var builder = new StringBuilder("new Dictionary<ulong, (string Name, string Description)>()\n\t{\n");
+        var builder = new StringBuilder("new Dictionary<ulong, (string Name, string? Description)>()\n\t{\n");
         var document = JsonDocument.Parse(json);
         foreach (var property in document.RootElement.EnumerateObject())
         {
@@ -28,6 +28,6 @@ protected override (string Type, string Source) Parse(string json)
         }
 
         builder.Append("\t}");
-        return ("IReadOnlyDictionary<ulong, (string Name, string Description)>", builder.ToString());
+        return ("IReadOnlyDictionary<ulong, (string Name, string? Description)>", builder.ToString());
     }
 }