build(deps): 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/ci.yml

@@ -19,7 +19,7 @@ jobs:
         # See top README for MSRV policy
         rust-version: [1.85.0, stable]
     steps:
-      - uses: actions/checkout@v6
+      - uses: actions/checkout@v7
 
       # Downgrade all dependencies to their minimum version, both to ensure our
       # minimum version bounds are correct and buildable, as well as to satisfy
@@ -109,7 +109,7 @@ jobs:
   format:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v6
+      - uses: actions/checkout@v7
 
       - name: Format
         run: cargo fmt --all -- --check