chore(deps): bump actions/checkout from 4 to 5

Bumps [actions/checkout](https://github.com/actions/checkout) from 4 to 5.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v4...v5)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-version: '5'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

.github/workflows/backend-ci.yml

@@ -19,7 +19,7 @@ jobs:
 
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v5
         with:
           fetch-depth: 0  # full history for branch diff logic
 

.github/workflows/backend-coverage.yml

@@ -16,7 +16,7 @@ jobs:
       pull-requests: write
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v5
         with:
           fetch-depth: 0
 

.github/workflows/ci-guard.yml

@@ -10,7 +10,7 @@ jobs:
     runs-on: ubuntu-latest
     if: ${{ !contains(toJson(github.event.pull_request.labels.*.name), 'ci-change-ok') }}
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
         with: { fetch-depth: 0 }
       - name: Fail if backend-ci.yml changed
         run: |