Fix assignment type error throwing exception

Upsilon/Binder/Binder.cs

@@ -155,8 +155,7 @@ namespace Upsilon.Binder
                 if (boundExpression.Type != variable.Type)
                 {
                     _diagnostics.LogCannotConvert(boundExpression.Type, variable.Type, e.Span);
-                    throw new NotImplementedException();
-                    //return boundExpression;
+                    return new BoundExpressionStatement(boundExpression);
                 }
             }