Properly handle full composite key binding in for loops

Upsilon/Binder/Binder.cs

@@ -959,6 +959,9 @@ namespace Upsilon.Binder
             VariableSymbol valueVariable;
             if (boundEnumerableExpression.Type is CompositeTypeContainer composite && composite.Types.Length == 2)
             {
+                var keyType = composite.Types[0];
+                keyVariable.TypeContainer = keyType;
+
                 var type = composite.Types[1];
                 if (type == Type.UserData)
                 {