The prior `package_version_is_current_hotfix_release` test was a
brittle hardcoded `assert_eq!(env!("CARGO_PKG_VERSION"), "0.8.22")`
that needed manual update on every release and only restated what
`scripts/release/check-versions.sh` already enforces.
Replace with `changelog_entry_exists_for_current_package_version`,
which reads `CHANGELOG.md` and asserts a `## [X.Y.Z]` entry exists
for the current `CARGO_PKG_VERSION`. No hardcoded version string —
this self-updates with the workspace version bump and gates against
the actual class of bug we just patched (the v0.8.21 / v0.8.22
backfill gap).
Hunter Bown
cd78b41fa3