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](actions/checkout@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>

Author: dependabot[bot]

.github/workflows/DocsCleanup.yml

@@ -16,7 +16,7 @@ jobs:
       contents: write
     steps:
       - name: Checkout gh-pages branch
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
         with:
           ref: gh-pages
       - name: Delete preview and history + push changes

.github/workflows/Documentation.yml

@@ -20,7 +20,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       # # Install all required X11 and OpenGL libraries
       # # These are needed for GLMakie to work in a headless environment

.github/workflows/Downgrade.yml

@@ -18,7 +18,7 @@ jobs:
         downgrade_mode: ['alldeps']
         julia-version: ['1.10']
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - uses: julia-actions/setup-julia@v2
         with:
           version: ${{ matrix.julia-version }}

.github/workflows/SpellCheck.yml

@@ -8,6 +8,6 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout Actions Repository
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
       - name: Check spelling
         uses: crate-ci/typos@v1.18.0