chore(deps): 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/continuous-integration.yml

@@ -28,7 +28,7 @@ jobs:
 
     steps:
       - name: "Checkout repository"
-        uses: "actions/checkout@v5"
+        uses: "actions/checkout@v6"
 
       - name: "Install PHP"
         uses: "shivammathur/setup-php@v2"
@@ -53,7 +53,7 @@ jobs:
 
     steps:
       - name: "Checkout repository"
-        uses: "actions/checkout@v5"
+        uses: "actions/checkout@v6"
 
       - name: "Install PHP"
         uses: "shivammathur/setup-php@v2"
@@ -86,7 +86,7 @@ jobs:
 
     steps:
       - name: "Checkout repository"
-        uses: "actions/checkout@v5"
+        uses: "actions/checkout@v6"
 
       - name: "Install dependencies (apt)"
         run: |
@@ -116,7 +116,7 @@ jobs:
 
     steps:
       - name: "Checkout repository"
-        uses: "actions/checkout@v5"
+        uses: "actions/checkout@v6"
 
       - name: "Install dependencies (apt)"
         run: |
@@ -178,7 +178,7 @@ jobs:
           git config --system core.eol lf
 
       - name: "Checkout repository"
-        uses: "actions/checkout@v5"
+        uses: "actions/checkout@v6"
 
       - name: "Install dependencies (apt)"
         if: ${{ matrix.operating-system == 'ubuntu-latest' }}