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)
- [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/release_gem.yml

@@ -22,7 +22,7 @@ jobs:
         with:
           egress-policy: audit
 
-      - uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
+      - uses: actions/checkout@1af3b93b6815bc44a9784bd300feb67ff0d1eeb3 # v6.0.0
 
       - name: Set up Ruby
         uses: ruby/setup-ruby@eaecf785f6a34567a6d97f686bbb7bccc1ac1e5c # v1.237.0

.github/workflows/test.yml

@@ -33,7 +33,7 @@ jobs:
       BUNDLE_GEMFILE: gemfiles/${{ matrix.gemfile }}.gemfile
 
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           submodules: "true"