Bump actions/checkout from 4 to 6 (#711)

Bumps [actions/checkout](https://github.com/actions/checkout) from 4 to 6.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v4...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_docs.yml

@@ -12,7 +12,7 @@ jobs:
     permissions:
       contents: write
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - name: Set up Ruby
         uses: ruby/setup-ruby@v1
         with:

.github/workflows/push_gem.yml

@@ -14,7 +14,7 @@ jobs:
       - uses: rubygems/configure-rubygems-credentials@main
         with:
           role-to-assume: ${{ secrets.RUBYGEMS_PUSH_ROLE }}
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - name: Set remote URL
         run: |
           # Attribute commits to the last committer on HEAD

.github/workflows/test.yml

@@ -16,7 +16,7 @@ jobs:
     timeout-minutes: 30
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - name: Set up Ruby
         uses: ruby/setup-ruby@v1
         with:
@@ -62,7 +62,7 @@ jobs:
     env:
       BUNDLE_GEMFILE: ${{ matrix.gemfile }}
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Set up Ruby
         uses: ruby/setup-ruby@v1
@@ -89,7 +89,7 @@ jobs:
     needs: test
     if: success()
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Download coverage reports from the test job
         uses: actions/download-artifact@v4
@@ -104,7 +104,7 @@ jobs:
     timeout-minutes: 30
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - name: Set up Ruby
         uses: ruby/setup-ruby@v1
         with: