Bump actions/checkout from 3 to 4

Bumps [actions/checkout](https://github.com/actions/checkout) from 3 to 4.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](https://github.com/actions/checkout/compare/v3...v4)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

.github/workflows/build.yml

@@ -13,7 +13,7 @@ jobs:
 
     steps:
     - name: Checkout code
-      uses: actions/checkout@v3
+      uses: actions/checkout@v4
 
     - name: Set up Ruby ${{ matrix.ruby }}
       uses: ruby/setup-ruby@v1

.github/workflows/docker.yml

@@ -15,7 +15,7 @@ jobs:
 
     steps:
       - name: checkout sources
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       - name: Set tag to latest
         if: (github.event_name == 'push' && github.ref == 'refs/heads/master') || github.event_name == 'schedule'

.github/workflows/gempush.yml

@@ -10,7 +10,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
     - name: Set up Ruby 2.6
       uses: ruby/setup-ruby@v1
       with: