release notes for 1.62.0 did not mention const_extern_fn stabilization

[tspiteri]

In version 1.62.0, const_extern_fn was stabilized for the "Rust" and "C" ABIs but I couldn't find an item in the release notes.

For what it's worth, the reference version 1.62.0 is updated from version 1.61.0 to reflect this stabilization.