ci: move the docs deploy off the deprecated Node 20 actions

The first Pages deploy succeeded but annotated every step: actions/checkout@v4,
setup-node@v4, upload-pages-artifact@v3, and deploy-pages@v4 all target Node 20
and are being force-run on Node 24. checkout@v6 matches what the rest of the
workflows in this repo already use.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VhyNvEWUgY8ALVacdJHxVJ

Author: rob-p

.github/workflows/docs.yml

@@ -22,8 +22,8 @@ jobs:
   build:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
-      - uses: actions/setup-node@v4
+      - uses: actions/checkout@v6
+      - uses: actions/setup-node@v7
         with:
           node-version: 22
           cache: npm
@@ -34,7 +34,7 @@ jobs:
       - name: Build site
         run: npm run build
         working-directory: docs-site
-      - uses: actions/upload-pages-artifact@v3
+      - uses: actions/upload-pages-artifact@v5
         with:
           path: docs-site/dist
 
@@ -46,4 +46,4 @@ jobs:
       url: ${{ steps.deployment.outputs.page_url }}
     steps:
       - id: deployment
-        uses: actions/deploy-pages@v4
+        uses: actions/deploy-pages@v5