chore(deps): bump actions/checkout from 4 to 6

Bumps [actions/checkout](https://github.com/actions/checkout) from 4 to 6.
- [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...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>

.github/workflows/bench-regression.yml

@@ -71,7 +71,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout (recursive — wifi-densepose-rufield path-deps vendor/rufield)
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
         with:
           # The workspace includes `wifi-densepose-rufield`, which path-deps the
           # `vendor/rufield` submodule crates. Without a recursive checkout the
@@ -150,7 +150,7 @@ jobs:
     needs: [bench-compile]
     steps:
       - name: Checkout (recursive)
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
         with:
           submodules: recursive