chore(deps): bump actions/checkout from 5 to 6

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]>

Author: dependabot[bot]

.github/workflows/ci.yml

@@ -35,7 +35,7 @@ jobs:
           - { rust: stable, os: ubuntu-22.04 }
     steps:
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           submodules: true
       - uses: dtolnay/rust-toolchain@stable
@@ -68,7 +68,7 @@ jobs:
           - { rust: nightly-2025-04-09, os: ubuntu-22.04 }
     steps:
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           submodules: true
       - uses: dtolnay/rust-toolchain@stable
@@ -88,7 +88,7 @@ jobs:
           - { rust: stable, os: ubuntu-22.04 }
     steps:
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           submodules: true
       - uses: dtolnay/rust-toolchain@stable
@@ -103,7 +103,7 @@ jobs:
     runs-on: ubuntu-22.04
     steps:
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           submodules: true
       - uses: dtolnay/rust-toolchain@stable
@@ -130,7 +130,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Check source code
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: AutoCorrect
         uses: huacnlee/autocorrect-action@v2