ci: bump actions/checkout from 6 to 7

Bumps [actions/checkout](https://github.com/actions/checkout) from 6 to 7.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](https://github.com/actions/checkout/compare/v6...v7)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-version: '7'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

.github/workflows/backport.yml

@@ -40,7 +40,7 @@ jobs:
           permission-contents: write
           permission-pull-requests: write
 
-      - uses: actions/checkout@v6
+      - uses: actions/checkout@v7
         with:
           ref: ${{ github.event.pull_request.head.sha }}
           token: ${{ steps.app-token.outputs.token }}

.github/workflows/doc.yml

@@ -28,7 +28,7 @@ jobs:
       url: ${{ steps.deployment.outputs.page_url }}
 
     steps:
-      - uses: actions/checkout@v6
+      - uses: actions/checkout@v7
         with:
           persist-credentials: false
 

.github/workflows/request-reviewers.yml

@@ -16,7 +16,7 @@ jobs:
     runs-on: ubuntu-24.04
     if: vars.APP_ID
     steps:
-      - uses: actions/checkout@v6
+      - uses: actions/checkout@v7
         with:
           ref: ${{ github.base_ref }}
 

.github/workflows/update-flake.yml

@@ -26,7 +26,7 @@ jobs:
           permission-contents: write
           permission-pull-requests: write
 
-      - uses: actions/checkout@v6
+      - uses: actions/checkout@v7
         with:
           ref: ${{ matrix.branch }}
           token: ${{ steps.generate-token.outputs.token }}