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

@@ -41,7 +41,7 @@ jobs:
             experimental: true
 
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
 
       - uses: shivammathur/setup-php@v2
         with:

.github/workflows/functional.yml

@@ -35,7 +35,7 @@ jobs:
             experimental: true
 
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
 
       - uses: shivammathur/setup-php@v2
         with:

.github/workflows/lint.yml

@@ -22,7 +22,7 @@ jobs:
           - "nightly"
 
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
 
       - uses: shivammathur/setup-php@v2
         with:

.github/workflows/phpstan.yml

@@ -21,7 +21,7 @@ jobs:
           - "8.1"
 
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
 
       - uses: shivammathur/setup-php@v2
         with: