Update integration-guidelines.md

[elvismdev]

Update the property name to the correct one to obtain the current post object ID; otherwise, it returns nothing.

Update the @type key; otherwise, it will not appear in the ld+json script.

Fixes #

Summary

Relevant technical choices

Technical choices that affect more than this issue:

Test instructions

This PR can be acceptance tested by following these steps:
1.
1.
1.

Quality assurance

• Security - I have thought about any security implications this code might add.
• Performance - I have checked that this code doesn't impact performance (greatly).
• Caching - I have analyzed the caching methods that this code touches and have added instructions to deal with those.
• Tested - I have tested this code to the best of my abilities.
• Automated tests - I have added unit tests to verify the code works as intended.
• Testability - I have added unique ids to elements, so they can be located in automated testing.
• I have altered a filename.
  • I have adjusted the ID property accordingly and updated all internal links.
  • I have added the redirect to the _redirects file in the root of the project.

[mhkuu]

Thanks a lot for the patch @elvismdev!

• The id vs. post_id-part: I guess id would indeed be more generic (e.g. for a term), but in this specific example post_id should work, right? Disclaimer: I did not run the code myself yet, I am trying to clean up the list of PRs 😄
• The @-part was fixed through Fixes typo in integration-guidelines.md #306.