Bump actions/checkout from 5 to 6 (#726)

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

Author: dependabot[bot]

.github/workflows/deploy.yml

@@ -9,7 +9,7 @@ jobs:
   deploy:
     runs-on: ubuntu-24.04
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - run: cargo install mdbook --version 0.4.40
       - run: cd mdbook && mdbook build
       - uses: JamesIves/github-pages-deploy-action@v4

.github/workflows/miri.yml

@@ -9,7 +9,7 @@ jobs:
     name: cargo miri test on ubuntu, rust nightly
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: actions-rust-lang/setup-rust-toolchain@v1
         with:
           toolchain: nightly

.github/workflows/release-plz.yml

@@ -15,7 +15,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           fetch-depth: 0
       - name: Install Rust toolchain

.github/workflows/test.yml

@@ -19,7 +19,7 @@ jobs:
     name: cargo test on ${{ matrix.os }}, rust ${{ matrix.toolchain }}
     runs-on: ${{ matrix.os }}-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: actions-rust-lang/setup-rust-toolchain@v1
         with:
           toolchain: ${{ matrix.toolchain }}
@@ -34,7 +34,7 @@ jobs:
     name: Cargo clippy
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: actions-rust-lang/setup-rust-toolchain@v1
         with:
           components: clippy