Add E2E tests for denying via WP Consent API

[tomalec]

Changes proposed in this Pull Request:

This is a small add-on to #429.
So, we test that a visitor can also deny their consent using the WP Consent API.

Checks:

• Does your code follow the WordPress coding standards?
• Have you written new tests for your changes, as applicable?
• Have you successfully run tests with your changes locally?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

Screenshots:

Detailed test instructions:

1. Checkout add/wp-consent-api-integration-tests-2 and build extension
2. Setup E2E environment and run tests
3. Confirm all tests pass

[eason9487]

Thanks for adding more test cases. I can run all E2E tests successfully. LGTM.

The only comment is not a blocker