Fix stabilization version for `bindings_after_at`
Fix stabilization version for `bindings_after_at`

According to the release notes and its PR milestone, it was stabilized
in 1.56.0.

aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust