docs(changelog): Call out cargo-new lockfile change

I was looking for what release this happened in but we didn't have it
listed.
We do list the documentation change.
This was likely from the PR focusing on the entire policy change which
made it easy to overlook each aspect of the policy change.

Author: epage

CHANGELOG.md

@@ -474,6 +474,8 @@
   [#12515](https://github.com/rust-lang/cargo/pull/12515)
 - ❗️ cargo-clean: error out if `--doc` is mixed with `-p`.
   [#12637](https://github.com/rust-lang/cargo/pull/12637)
+- ❗ cargo-new / cargo-init no longer exclude `Cargo.lock` in VCS ignore files for libraries.
+  [#12382](https://github.com/rust-lang/cargo/pull/12382)
 - cargo-update: silently deprecate `--aggressive` in favor of the new `--recursive`.
   [#12544](https://github.com/rust-lang/cargo/pull/12544)
 - cargo-update: `-p/--package` can be used as a positional argument.