Bump actions/checkout to v4

Author: jbampton

.github/workflows/rail_inspector.yml

@@ -16,7 +16,7 @@ jobs:
     name: rail_inspector tests
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - uses: ruby/setup-ruby@v1
         with:
           ruby-version: 3.2