Bump WordPress "tested up to" version 6.6

[ankitguptaindia]

Description of the Change

This PR bumps the WP tested up to version 6.6, and bumps the WP min to 6.4.

Closes #174

How to test the Change

Changelog Entry

Changed - Bump WordPress "tested up to" version 6.6.
Changed - Bump WordPress minimum from 6.3 to 6.4.

Credits

Props @ankitguptaindia

Checklist:

• I agree to follow this project's Code of Conduct.
• I have updated the documentation accordingly.
• I have added tests to cover my change.
• All new and existing tests pass.

[dkotter]

We'll need to bump our minimum WordPress version in our E2E tests as well. Those are failing right now because it's using WordPress 6.3 and the plugin can't be installed there anymore: https://github.com/10up/insecure-content-warning/blob/develop/.github/workflows/cypress.yml#L47

[jeffpaul]

Still seeing e2e test failures, guessing that's another wp-env / dependency update that's needed?

[ankitguptaindia]

Hello @dkotter I updated WP Min version and wp-env version but tests are still failing here. COuld you check or suggest changes here? thank you!

[dkotter]

Hello @dkotter I updated WP Min version and wp-env version but tests are still failing here. COuld you check or suggest changes here? thank you!

This seems to be the same issue Dharmesh mentions here: #172 (review). So this looks good to me