Post list tables row headers changed

π **Source:** [Post list tables row headers changed]()
## Highlights
- This change significantly improves accessibility for post list tables by ensuring that the naming used for screen readers to identify the current row refers consistently to the name of the relevant post, rather than referring to a selection checkbox that may not be present if the post is not currently available for editing.
- Note: The semantic row header now names the post consistently, even when edit permissions remove the checkbox.
- Retaining both td and th selectors will support retaining compatibility with versions of WordPress prior to 7.1.
- Note: Extensions supporting older WordPress releases should allow both old and new table-cell elements.