ci: cancel superseded actionlint and skill-docs runs

actionlint.yml and skill-docs.yml trigger on both push and pull_request
with no concurrency group, so every push to an active branch left the
previous (now-obsolete) runs queued or running — twice per commit on
same-repo PR branches. Add the same cancel-in-progress concurrency
groups the heavier workflows already use, plus a free static tripwire
test that fails CI if a push+pull_request workflow ever ships again
without cancel-in-progress.

Contributed by @jbetala7 (PR #2053).

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

.github/workflows/actionlint.yml

@@ -1,5 +1,13 @@
 name: Workflow Lint
 on: [push, pull_request]
+
+# Cancel superseded runs for the same branch (matches evals.yml,
+# windows-free-tests.yml, etc.). head_ref is set on pull_request; ref_name is
+# the fallback for push so a rapid push series doesn't pile up stale lint runs.
+concurrency:
+  group: actionlint-${{ github.head_ref || github.ref_name }}
+  cancel-in-progress: true
+
 jobs:
   actionlint:
     runs-on: ubicloud-standard-8

.github/workflows/skill-docs.yml

@@ -1,5 +1,13 @@
 name: Skill Docs Freshness
 on: [push, pull_request]
+
+# Cancel superseded runs for the same branch (matches evals.yml,
+# windows-free-tests.yml, etc.). head_ref is set on pull_request; ref_name is
+# the fallback for push so a rapid push series doesn't pile up stale runs.
+concurrency:
+  group: skill-docs-${{ github.head_ref || github.ref_name }}
+  cancel-in-progress: true
+
 jobs:
   check-freshness:
     runs-on: ubicloud-standard-8