Add an advisory CI job on latest stable

Pinning CI meant a future Rust release could break the build without
anyone noticing until the pin moved. This job tracks latest stable and
runs the test suite and clippy, so that breakage is visible early.

Marked `continue-on-error`, so it reports rather than gates: a new
clippy lint landing in stable should not fail a pull request that did
not cause it. The pinned `test` job remains the gate.

Note that GitHub renders a `continue-on-error` job as passing with an
annotation rather than as failed. If it should be more visible, make it
a required check and drop the flag.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

CHANGELOG.md

@@ -12,7 +12,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - A declared minimum supported Rust version of **1.88**, verified by running
   the test suite against it. The floor comes from the dependency graph
   (`reqwest` → `url` → `idna` → `icu_*`), not from this crate's own code.
-  CI builds on both the MSRV and the pinned dev toolchain.
+  CI builds on both the MSRV and the pinned dev toolchain, plus an advisory
+  job on latest stable that reports breakage from a new Rust release
+  without gating pull requests.
 - Wrappers for every one of the API's 34 `Route::resource` groups, plus
   `users` — 265 methods. See `COVERAGE.md` for the per-endpoint inventory.
 - `COVERAGE.md`, a detailed record of what is wrapped, what is not, and why,