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/continuous-integration.yml

@@ -22,7 +22,7 @@ jobs:
       cancel-in-progress: true
       group: ${{ github.workflow }}-build-${{ github.event.pull_request.number || github.ref }}-${{ matrix.os }}
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: dtolnay/rust-toolchain@stable
         with:
           toolchain: stable
@@ -33,7 +33,7 @@ jobs:
       cancel-in-progress: true
       group: ${{ github.workflow }}-lint-${{ github.event.pull_request.number || github.ref }}
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: dtolnay/rust-toolchain@stable
         with: 
           toolchain: stable
@@ -50,7 +50,7 @@ jobs:
       cancel-in-progress: true
       group: ${{ github.workflow }}-test-${{ github.event.pull_request.number || github.ref }}
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: dtolnay/rust-toolchain@stable
       - uses: taiki-e/install-action@v2 # don't use taiki-e/cache-cargo-install-action, compiled version already available (https://github.com/taiki-e/install-action/blob/main/TOOLS.md)
         with:
@@ -62,7 +62,7 @@ jobs:
       cancel-in-progress: true
       group: ${{ github.workflow }}-fmt-${{ github.event.pull_request.number || github.ref }}
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: dtolnay/rust-toolchain@stable
         with: 
           toolchain: stable
@@ -81,7 +81,7 @@ jobs:
       cancel-in-progress: true
       group: ${{ github.workflow }}-cargo-deny-checks-${{ github.event.pull_request.number || github.ref }}
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: dtolnay/rust-toolchain@stable
         with: 
           toolchain: stable