ci: bump actions/checkout from 5 to 6 (#652)

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

Author: dependabot[bot]

.github/workflows/ci.yml

@@ -26,7 +26,7 @@ jobs:
       DATABASE_URL: postgres://postgres:postgres@localhost:5432/postgres
       SENTRY_ENVIRONMENT: CI
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: actions/setup-node@v6
         with:
           node-version: 20
@@ -61,7 +61,7 @@ jobs:
       DATABASE_URL: postgres://postgres:postgres@localhost:5432/postgres
       SENTRY_ENVIRONMENT: CI
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: actions/setup-node@v6
         with:
           node-version: 20
@@ -81,7 +81,7 @@ jobs:
       REGISTRY: ghcr.io
       SENTRY_ENVIRONMENT: CI
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
 
       - uses: docker/login-action@v3
         with:
@@ -101,7 +101,7 @@ jobs:
     needs: [build, 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 --build-arg GIT_COMMIT=$(git rev-parse HEAD)
         env: