My reasoning is as follows: we need an up-to-date rust-overlay in order
to access recent nightlies. Currently we follow crane's rust-overlay,
but recent versions of crane don't have a rust-overlay input anymore. So
we'll need to have rust-overlay as input like this eventually anyway.
Hence I did this without even updating crane because there was no need.

This is not breaking anything on hax, but unbreaks `serde`: serde-rs/serde#2734