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/polish-the-code.yml

@@ -29,7 +29,7 @@ jobs:
     # Limit the running time
     timeout-minutes: 10
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           ref: ${{ github.event.pull_request.head.sha }} # checkout PR HEAD commit
           fetch-depth: 0 # required for merge-base check

action.yml

@@ -52,7 +52,7 @@ runs:
       shell: bash
 
     - name: Checkout code
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
       with:
         ref: ${{ github.ref }} # Fetch latest changes (even by previous job)
         fetch-depth: 0 # Fetch all history for all branches and tags. Otherwise github.event.pull_request.base.ref SHA isn't found.