CI: skip the test (windows-latest) gate in cancelled runs

With always() the gate also ran when a newer push cancelled the run,
taking a runner slot only to report a red check on the superseded
commit. !cancelled() still runs it when a test leg fails (a skipped
required check would count as passing), but not in a cancelled run.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.github/workflows/ci.yml

@@ -201,7 +201,7 @@ jobs:
   windows-gate:
     name: test (windows-latest)
     needs: [platforms, test]
-    if: always()
+    if: ${{ !cancelled() }}
     runs-on: ubuntu-latest
     steps:
       - env: