chore: 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/doc.yml

@@ -24,7 +24,7 @@ jobs:
   doc:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           ref: ${{ github.ref }}
       - name: Set up Ruby

.github/workflows/publish-gem.yml

@@ -15,7 +15,7 @@ jobs:
       GEM_HOST_API_KEY: ${{ secrets.RUBYGEMS_AUTH_TOKEN }}
       GEM_HOST_OTP_CODE: ${{ github.event.inputs.rubygems-otp-code }}
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
       with:
           fetch-depth: 0
 

.github/workflows/release.yml

@@ -26,7 +26,7 @@ jobs:
           version-file: "lib/rgl/version.rb"
 
       # Checkout code if release was created
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         if: ${{ steps.release.outputs.release_created }}
       # Setup ruby if a release was created
       - uses: ruby/setup-ruby@v1

.github/workflows/test.yml

@@ -21,7 +21,7 @@ jobs:
           - jruby-head
 
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Set up Ruby
         uses: ruby/setup-ruby@v1
         with: