build(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] <[email protected]>

Author: dependabot[bot]

.github/workflows/emacs-eask.yml

@@ -17,7 +17,7 @@ jobs:
 
     steps:
     - name: Check out the source code
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
 
     - name: Install Emacs
       uses: jcs090218/setup-emacs@master

.github/workflows/emacs-eldev.yml

@@ -29,7 +29,7 @@ jobs:
       uses: emacs-eldev/setup-eldev@v1
 
     - name: Check out the source code
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
 
     - name: Ensure that copyright notices are up-to-date
       run: ${ELDEV} ${ELDEV_ARGS} doctor up-to-date-copyright --all-tests

.github/workflows/melpazoid.yml

@@ -12,7 +12,7 @@ jobs:
 
     steps:
     - name: Checkout
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
 
     - name: Set up Emacs
       uses: jcs090218/setup-emacs@master