Add integration tests for indexable creation

[leonidasmi]

What is the goal of this issue?

To increase integration test coverage in an area where we lacking currently, in the indexable creation flow

What needs to be done to achieve the goal?

Like this PR, we can start covering all the cases where indexable are and aren't created upon a post/attachment/term/etc creation.

Does the issue still need UX or research?

If available: what are the tips for fixing the problem or possible solutions?

What is the expected result/behavior?

Should documentation be added or updated for this change? and if so, where?

### Tasks
- [ ] https://github.com/Yoast/wordpress-seo/issues/21390