py::enum_ is deprecated

[nsmith-]

To expose the parsed TFormula nodes for use in downstream libraries like correctionlib-gradients, we expose py::enum_ types such as

correctionlib/src/python.cc

Lines 141 to 146 in f5c490f

	py::enum_<FormulaAst::NodeType>(formula_ast, "NodeType")
	.value("LITERAL", FormulaAst::NodeType::Literal)
	.value("VARIABLE", FormulaAst::NodeType::Variable)
	.value("PARAMETER", FormulaAst::NodeType::Parameter)
	.value("UNARY", FormulaAst::NodeType::Unary)
	.value("BINARY", FormulaAst::NodeType::Binary);

As of pybind11 v3, these are deprecated in favor of py::native_enum
See https://pybind11.readthedocs.io/en/stable/classes.html#enumerations-and-internal-types for details.