When `--experimental-dual-fund` is enabled upfront shutdown_scriptpubkey does not follow bolt

I've been doing some early testing with our in-progress dual-funding implementation in LDK, and it seems that the (mis)behaviour described in https://github.com/ElementsProject/lightning/issues/3815 comes up again when `--experimental-dual-fund` flag is set for Core Lightning and attempting to open an outbound dual-funded channel to LDK.

I'll provide a repro if needed but it would involve an in-progress fork of our `ldk-sample` node. Logs are the same as #3815, with LDK failing the channel after receiving `open_channel2` due to `shutdown_scriptpubkey` TLV not being set by CLN when both nodes advertise `option_upfront_shutdown_script`.

Apologies for necromancing!