One missed case, Python 2 only.

Author: rwgk

include/pybind11/cast.h

@@ -778,7 +778,7 @@ struct pyobject_caster {
         // For Python 2, without this implicit conversion, Python code would
         // need to be cluttered with six.ensure_text() or similar, only to be
         // un-cluttered later after Python 2 support is dropped.
-        if (std::is_same<T, str>::value && isinstance<bytes>(src)) {
+        if (constexpr_bool(std::is_same<T, str>::value) && isinstance<bytes>(src)) {
             PyObject *str_from_bytes = PyUnicode_FromEncodedObject(src.ptr(), "utf-8", nullptr);
             if (!str_from_bytes) throw error_already_set();
             value = reinterpret_steal<type>(str_from_bytes);