Bump actions/checkout from 5 to 6

Bumps [actions/checkout](https://github.com/actions/checkout) from 5 to 6.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v5...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/demo_page.yml

@@ -9,7 +9,7 @@ jobs:
       - name: Dependencies 🔧
         run: sudo apt-get install imagemagick jhead
       - name: Checkout 🛎️
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - name: Build 🖼️
         run: |
           ls -lah

.github/workflows/macos.yml

@@ -17,7 +17,7 @@ jobs:
         run: brew install imagemagick jhead
 
       - name: Checkout 🛎️
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Get assert.sh 🎁
         run: curl -f "https://raw.githubusercontent.com/lehmannro/assert.sh/v1.1/assert.sh" -o assert.sh

.github/workflows/shellcheck.yml

@@ -25,7 +25,7 @@ jobs:
 
       # Checks-out your repository under $GITHUB_WORKSPACE, so your job can access it
       - name: Checkout 🛎️
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       # Run ShellCheck
       - name: ShellCheck 🔎

.github/workflows/ubuntu.yml

@@ -18,7 +18,7 @@ jobs:
         run: sudo apt-get install imagemagick jhead
 
       - name: Checkout 🛎️
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Get assert.sh 🎁
         run: curl -f "https://raw.githubusercontent.com/lehmannro/assert.sh/v1.1/assert.sh" -o assert.sh