Bump actions/checkout from v4 to v5 to fix Node.js 20 deprecation warning

Agent-Logs-Url: https://github.com/m-aciek/python-docs-offline/sessions/a51b39f3-45b2-4f1e-a9a0-4dc19d28b22a

Co-authored-by: m-aciek <9288014+m-aciek@users.noreply.github.com>

Author: Copilot

.github/workflows/build.yaml

@@ -186,7 +186,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout gh-pages branch
-        uses: actions/checkout@v4
+        uses: actions/checkout@v5
         with:
           ref: gh-pages
           path: gh-pages