Restore default for column_valued name parameter (#260)

Commit 20436f7 (#258) incorrectly
removed this default, which is needed to accept calls without a name,
i.e., .column_valued().

Fixes #259.

Signed-off-by: Anders Kaseorg <andersk@mit.edu>

sqlalchemy-stubs/sql/functions.pyi

@@ -59,7 +59,7 @@ class FunctionElement(  # type: ignore[misc]
     ) -> ScalarFunctionColumn[_TE]: ...
     def table_valued(self, *expr: Any, **kw: Any) -> TableValuedAlias: ...  # type: ignore[override]
     def column_valued(
-        self, name: Optional[Any], joins_implicitly: bool = False
+        self, name: Optional[Any] = ..., joins_implicitly: bool = False
     ) -> TableValuedColumn[Any]: ...
     @property
     def columns(self) -> ColumnCollection[ColumnElement[Any]]: ...  # type: ignore[override]