Bump actions/checkout from 4 to 7

Bumps [actions/checkout](https://github.com/actions/checkout) from 4 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/v4...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/ci.yml

@@ -26,7 +26,7 @@ jobs:
       # DB/queue tests use this instead of an ephemeral instance.
       TEST_DATABASE_URL: postgresql://postgres:postgres@localhost:5432/ditto_site
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v7
       - uses: actions/setup-node@v4
         with:
           node-version: 22