ci: bump actions/checkout from 5 to 6 (#278)

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>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/ci.yml

@@ -25,7 +25,7 @@ jobs:
       DATABASE_URL: postgres://postgres:postgres@localhost:5432/spark_deal_observer
       NPM_CONFIG_WORKSPACE: api
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: actions/setup-node@v6
         with:
           node-version: 20
@@ -54,7 +54,7 @@ jobs:
       NPM_CONFIG_WORKSPACE: backend
       GLIF_TOKEN: ${{ secrets.GLIF_TOKEN }}
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: actions/setup-node@v6
         with:
           node-version: 20
@@ -65,7 +65,7 @@ jobs:
   lint-all:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: actions/setup-node@v6
         with:
           node-version: 20
@@ -81,7 +81,7 @@ jobs:
     env:
       REGISTRY: ghcr.io
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
 
       - uses: docker/login-action@v3
         with:
@@ -101,7 +101,7 @@ jobs:
     needs: [build-api, build-backend, docker-build]
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: superfly/flyctl-actions/setup-flyctl@master
       - run: flyctl deploy --remote-only -c api/fly.toml
         env:
@@ -131,7 +131,7 @@ jobs:
     needs: [build-api, build-backend, docker-build]
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: superfly/flyctl-actions/setup-flyctl@master
       - run: flyctl deploy --remote-only -c backend/fly.toml
         env: