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] <support@github.com>

Author: dependabot[bot]

.github/workflows/autotag-releases.yml

@@ -15,7 +15,7 @@ jobs:
     permissions:
       contents: write
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Get version from tag
         id: tag_name
         run: |

.github/workflows/ci.yml

@@ -32,7 +32,7 @@ jobs:
           - "beta"
           - "stable"
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
 
       # Test toolchain file support
       - name: Write rust-toolchain.toml
@@ -93,7 +93,7 @@ jobs:
     name: Cache
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
 
       - name: Install Rust
         uses: ./