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/all-pr-tests.yml

@@ -32,7 +32,7 @@ jobs:
     # Name the job in the matrix
     name: "PR Tests PHP ${{ matrix.php }} WordPress ${{ matrix.wordpress }}"
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
 
       - name: Run General Tests
         # See https://github.com/alleyinteractive/action-test-general for more options

.github/workflows/update-changelog.yml

@@ -10,7 +10,7 @@ jobs:
 
     steps:
       - name: Checkout code
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           ref: main
 

.github/workflows/upgrade-wordpress-plugin.yml

@@ -12,7 +12,7 @@ jobs:
   update-plugin:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
     - uses: alleyinteractive/action-update-wordpress-plugin@v2.0.0
       with:
         plugin-file: 'plugin.php'