Bump actions/checkout from 4 to 6

Bumps [actions/checkout](https://github.com/actions/checkout) from 4 to 6.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](https://github.com/actions/checkout/compare/v4...v6)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

.github/workflows/publish-aichat-app.yaml

@@ -32,7 +32,7 @@ jobs:
           submodules: recursive
           fetch-depth: 0
       - name: Checkout intermediate Pages repo
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
         with:
           repository: IfcOpenShell/aichat_ifcopenshell_org_static_html
           ref: gh-pages

.github/workflows/publish-pyodide-demo-app.yml

@@ -32,7 +32,7 @@ jobs:
           submodules: recursive
           fetch-depth: 0
       - name: Checkout intermediate Pages repo
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
         with:
           repository: IfcOpenShell/wasm_ifcopenshell_org_static_html
           ref: gh-pages