Update Node version in actions/checkout (#864)

Addresses a deprecation warning in our CI workflows: 
```
Node.js 16 actions are deprecated. Please update the following actions to use Node.js 20: actions/checkout@v3. For more information see: https://github.blog/changelog/2023-09-22-github-actions-transitioning-from-node-16-to-node-20/.
```

.github/workflows/run-tests.yml

@@ -54,7 +54,7 @@ jobs:
         image: selenium/standalone-chrome:latest
         ports: ["4444:4444"]
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Install Ruby
         uses: ruby/setup-ruby@v1
         with: