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] <[email protected]>

Author: dependabot[bot]

.github/workflows/docs.yml

@@ -30,7 +30,7 @@ jobs:
         runs-on: ubuntu-latest
 
         steps:
-            -   uses: actions/checkout@v5
+            -   uses: actions/checkout@v6
                 with:
                     fetch-depth: 0
 

.github/workflows/test-docs.yml

@@ -19,7 +19,7 @@ jobs:
         runs-on: ubuntu-latest
 
         steps:
-            -   uses: actions/checkout@v5
+            -   uses: actions/checkout@v6
                 with:
                     fetch-depth: 0
 

.github/workflows/tests.yml

@@ -17,7 +17,7 @@ jobs:
 
         steps:
             -   name: Checkout code
-                uses: actions/checkout@v5
+                uses: actions/checkout@v6
 
             -   name: Setup PHP
                 uses: shivammathur/setup-php@v2
@@ -39,7 +39,7 @@ jobs:
 
         steps:
             -   name: Checkout code
-                uses: actions/checkout@v5
+                uses: actions/checkout@v6
 
             -   name: Setup PHP
                 uses: shivammathur/setup-php@v2
@@ -61,7 +61,7 @@ jobs:
 
         steps:
             -   name: Checkout code
-                uses: actions/checkout@v5
+                uses: actions/checkout@v6
 
             -   name: Setup PHP
                 uses: shivammathur/setup-php@v2