rule_compiler: fix error running on Python 3.14

Example error:
```
    ast.Str(s=node.attr),
    ^^^^^^^
AttributeError: module 'ast' has no attribute 'Str'
```

`ast.Str` was deprecated since 3.8 and was removed in 3.14, see https://docs.python.org/3/whatsnew/3.14.html#id9

src/ifcopenshell-python/ifcopenshell/express/rule_compiler.py

@@ -741,7 +741,7 @@ class AttributeGetattrTransformer(ast.NodeTransformer):
                 func=ast.Name(id="express_getattr", ctx=ast.Load()),
                 args=[
                     new_value,
-                    ast.Str(s=node.attr),
+                    ast.Constant(value=node.attr),
                     ast.Name(id="INDETERMINATE", ctx=ast.Load()),
                 ],
                 keywords=[],