Prepare code for breaking change in Protobuf C++ API.

Protobuf 6.30.0 will change the return types of Descriptor::name() and other
methods to absl::string_view. This makes the code work both before and after
such a change.

PiperOrigin-RevId: 715199813

pybind11_protobuf/proto_cast_util.cc

@@ -59,8 +59,8 @@ namespace {
 // Resolves the class name of a descriptor via d->containing_type()
 py::object ResolveDescriptor(py::object p, const Descriptor* d) {
   return d->containing_type() ? ResolveDescriptor(p, d->containing_type())
-                                    .attr(py::str(d->name()))
-                              : p.attr(py::str(d->name()));
+                                    .attr(py::str(std::string_view(d->name())))
+                              : p.attr(py::str(std::string_view(d->name())));
 }
 
 // Returns true if an exception is an import error.