Switch from action/checkout@2 to @4

Author: AlexB52

.github/workflows/ci.yml

@@ -30,7 +30,7 @@ jobs:
             ruby: 2.5
     name: Ruby ${{ matrix.ruby }} test (${{ matrix.os }})
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v4
     - name: Set up Ruby
       uses: ruby/setup-ruby@v1
       with:
@@ -54,7 +54,7 @@ jobs:
           - rspec-ruby
           - bundler-app
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - name: Set up Ruby
         uses: ruby/setup-ruby@v1
         with: