update actions/checkout to v4

Author: kenichiice

.github/workflows/test.yml

@@ -28,7 +28,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     # continue-on-error: ${{ endsWith(matrix.ruby, 'head') }}
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
     - uses: ruby/setup-ruby@v1
       with:
         ruby-version: ${{ matrix.ruby }}