chore(deps): bump actions/checkout from 4 to 7 (#804)

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

Author: dependabot[bot]

.github/workflows/l10n.yml

@@ -16,7 +16,7 @@ jobs:
     # Observed fleet-wide n=225: median 0.1 min, max 1.2 min. Bound loosely at 15.
     timeout-minutes: 15
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v7
       - uses: actions/setup-node@v4
         with:
           node-version: "22"

.github/workflows/merge-hygiene.yml

@@ -33,7 +33,7 @@ jobs:
     name: Conflict markers and PHP syntax
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v7
 
       # Conflict markers, anywhere in the tree we author. A marker means a merge
       # was committed half-finished; every downstream signal from that commit is