Disabled Publish button is clickable

[mmtr]

Describe the bug
As of #11543, PostPublishButton doesn't have a disabled attribute anymore, but uses aria-disabled instead. This is allowing to click on the button, when it shouldn't be possible (for example when the post content is empty).

To Reproduce

1. Start creating a new post
2. Note how the "Publish..." button is styled as disabled
3. Click on the "Publish..." button

Expected behavior
The Pre-publish checks sidebar shouldn't be opened since the Publish button is disabled. Furthermore, the "Publish" button displayed there is also disabled, but we can still click on it a save the post (note how the date change from "Immediately" to the current date).

Screenshots

Additional context
Issue found on Automattic/wp-calypso#29594 (props to @Copons).

[swissspidy]

Duplicate of #11809. PR: #11760.