fix post excerpt typo

[masteradhoc]

Context

• fix a typo for child pages post excerpt.
  See Reports https://wordpress.org/support/topic/excerpt-problem-9/ and Typo and logic issue for child excerpt #369

Fixes #369

Summary

This PR can be summarized in the following changelog entry:

• Fixes a bug where cloning an attachment did not copy its description as expected.
• Fixes a bug where cloning an attachment did not copy its caption as expected. Props to @masteradhoc.

Relevant technical choices:

Test instructions

Test instructions for the acceptance test before the PR gets merged

This PR can be acceptance tested by following these steps:

• in the Duplicate Post settings, under "Post/page elements to copy", select "Attachments" and save
• Create/edit a post
• add an image to it by uploading a new one
• make sure to edit the image in the media library modal and add alt. text, caption and decription.
• save the post
• clone the post
• check the media library page: you should get 2 copies of the image you uploaded
• edit both of them and check that both have the same values for alt. text, caption and description.
  • without this PR, caption and description were not copied at all.

Relevant test scenarios

• Changes should be tested with the browser console open
• Changes should be tested on different posts/pages/taxonomies/custom post types/custom taxonomies
• Changes should be tested on different editors (Default Block/Gutenberg/Classic/Elementor/other)
• Changes should be tested on different browsers
• Changes should be tested on multisite

Test instructions for QA when the code is in the RC

• QA should use the same steps as above.

QA can test this PR by following these steps:

Impact check

This PR affects the following parts of the plugin, which may require extra testing:

UI changes

• This PR changes the UI in the plugin. I have added the 'UI change' label to this PR.

Documentation

• I have written documentation for this change. For example, comments in the Relevant technical choices, comments in the code, documentation on Confluence / shared Google Drive / Yoast developer portal, or other.

Quality assurance

• I have tested this code to the best of my abilities
• I have added unittests to verify the code works as intended

Innovation

• No innovation project is applicable for this PR.
• This PR falls under an innovation project. I have attached the innovation label and noted the work hours.

Fixes #

[enricobattocchi]

Hey @masteradhoc, thanks for the patch!