CI: current actions, so the runner stops warning

actions/checkout and actions/setup-node at v4 target Node 20, which GitHub
runners now force onto Node 24 with a deprecation notice on every run. v5 of
both targets Node 24 natively. No change to what the workflow does.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Nh4A79bbqT9dcd2inzYUdg

.github/workflows/ci.yml

@@ -10,9 +10,9 @@ jobs:
   check:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
 
-      - uses: actions/setup-node@v4
+      - uses: actions/setup-node@v5
         with:
           node-version: '22'
           cache: npm