Allow autotweeting of scheduled posts.

[peterwilsoncc]

Description of the Change

Removes the current_user_can() check in the publish_tweet() function to account for cron jobs publishing a scheduled post.

The save_tweet_meta() function includes a current_user_can check so the data should not be manipulated by unauthorized users in the classic editor. The rest API endpoint uses the update_post_autoshare_for_twitter_meta_permission_check() function to implement the current_user_can() check.

I wasn't able to figure out how to test this without doing a large refactor of test_maybe_publish_tweet().

Closes #398

How to test the Change

1. Create a block editor post
2. Enable auto-tweet and an account to tweet from
3. Schedule the post for three minutes for now
4. Return to the All posts screen
5. Make a cup of tea or coffee stating from stone cold water in the kettle
6. Once the scheduled time has past, load a random screen in the WP Dashboard in order to trigger WP-Cron
7. Ensure the tweet is published
8. Enable the classic editor
9. Create a classic editor post
10. Enable auto-tweet and an account to tweet from
11. Schedule the post for three minutes for now
12. Return to the all posts screen
13. Pat the cat/dog for a few minutes explaining what a good cat/dog they are throughout
14. Once the scheduled time has past, load a random screen in the WP Dashboard in order to trigger WP-Cron
15. Ensure the tweet is published

Changelog Entry

Fixed - Bug preventing the autosharing of posts for scheduled posts.

Credits

Props @justinmaurerdotdev, @peterwilsoncc

Checklist:

• I agree to follow this project's Code of Conduct.
• I have updated the documentation accordingly.
• I have added Critical Flows, Test Cases, and/or End-to-End Tests to cover my change.
• All new and existing tests pass.