Tests: Only run chromedriver in headless mode on GitHub Actions

[n7studios]

Summary

Updates the EndToEnd.suite.yml to run chromedriver in headed mode by default, allowing developers to see the test steps, with GitHub actions using the headless environment to run chromedriver in headless mode.

Testing

Existing tests pass.

Checklist

• I have written a test and included it in this PR
• I have run all tests and they pass
• The code passes when running the PHP CodeSniffer
• Code meets WordPress Coding Standards for PHP, HTML, CSS and JS
• Security and Sanitization requirements have been followed
• I have assigned a reviewer or two to review this PR (if you're not sure who to assign, we can do this step for you)