cargo-semver-checks 0.12.0 is released w/ stability guarantee for stable and beta Rust

cargo-semver-checks is a linter checking for semver violations in crates' public API.

Previously, cargo-semver-checks needed nightly because generating rustdoc JSON is unstable.

As of v0.12.0, it now supports all rustdoc JSON format versions in stable and beta Rust. It uses RUSTC_BOOTSTRAP, so you no longer need nightly installed at all.

The GitHub Action has been updated accordingly and will no longer break on every new rustdoc format change in nightly.