chore(ci): repin the shared workflow to the stable-check-context revision

Picks up SecurityRonin/fleet-ci#9. Repin only -- no gate behaviour changes.

Two fixes, both of which only matter when a check context is REQUIRED:

  - A skipped job publishes its `name:` EXPRESSION, not the evaluated value.
    The coverage job's name was a multi-line ternary, so any repo turning the
    coverage gate off published a check named with the raw expression source,
    newlines included. That name is now the constant `Coverage`.

  - Matrix jobs cannot serve as required contexts, because GitHub appends the
    matrix values -- `MSRV (<crate>, <floor>)`, `Test (<os>)` -- so the context
    name moves whenever a crate is added or a floor is raised, and a required
    context that stops reporting makes every PR unmergeable with no
    explanation. The workflow now publishes an aggregate `All checks` job that
    needs all twelve others and whose name never varies.

`ci / All checks` becomes requirable once every repo carries this pin.

Author: h4x0r

.github/workflows/ci.yml

@@ -28,4 +28,4 @@ jobs:
   # no-op in practice — the fuzz crate is outside the workspace so llvm-cov
   # never reports it, and test code executes during the run it is measured by.
   ci:
-    uses: SecurityRonin/fleet-ci/.github/workflows/rust-ci.yml@f9802dca64a95eb881fd05dd3f4f16e53b97f2b3
+    uses: SecurityRonin/fleet-ci/.github/workflows/rust-ci.yml@9234e1fa9f85b14a8d6fddc7a8f7378f7e30b183