Migrate users of dynamic_cast/down_cast on protobuf types to use prot…

…obuf cast functions instead. These do not require RTTI to work.

PiperOrigin-RevId: 638352213

pybind11_protobuf/proto_caster_impl.h

@@ -55,7 +55,7 @@ struct proto_caster_load_impl {
     const ::google::protobuf::Message *message =
         pybind11_protobuf::PyProtoGetCppMessagePointer(src);
     if (message) {
-      value = dynamic_cast<const ProtoType *>(message);
+      value = ::google::protobuf::DynamicCastToGenerated<ProtoType>(message);
       if (value) {
         // If the capability were available, then we could probe PyProto_API and
         // allow c++ mutability based on the python reference count.