fix(ci): reference the unused-deps input by its declared name

The input is declared as `unused-deps` but the job is gated on
`inputs.unused_deps`. That property does not exist, so the expression is empty,
and the job has been skipped on every run since the feature was added in
2f2015e (2026-03-25) — `mix deps.unlock --check-unused` has never actually run.

Visible on any recent run of Ash's own CI: the job reports "skipped" in both
matrix legs despite the input defaulting to true. Nearby gates such as
`inputs.changelog-lint` use the hyphenated name directly and work, so this is
just the one identifier.

Author: joshprice

.github/workflows/ash-ci.yml

@@ -590,7 +590,7 @@ jobs:
   unused-deps:
     name: mix deps.unlock --check-unused
     runs-on: ubuntu-latest
-    if: ${{inputs.unused_deps}}
+    if: ${{inputs.unused-deps}}
     needs:
       - build-test
     steps: