Update checkout action version

Author: m-nakamura145

.github/workflows/ci.yml

@@ -22,7 +22,7 @@ jobs:
   rubocop:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
     - uses: ruby/setup-ruby@v1
       with:
         ruby-version: 3.2
@@ -75,7 +75,7 @@ jobs:
     env:
       BUNDLE_GEMFILE: gemfiles/active_support_${{ matrix.activesupport }}.gemfile
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
     - uses: ruby/setup-ruby@v1
       with:
         ruby-version: ${{ matrix.ruby }}