Fix category checkbox handler ID matching

[ffffelix]

Fixes category checkboxes in v6.7.1.

This change makes matching the desired tag ID to its checkbox elements more strict.

Example: when selecting a category with an ID of 1, the jQuery selector would also match the checkboxes for any category with an ID starting 1 (e.g. 10, 110, 1043).

The checkbox IDs are output via wp_unique_prefixed_id so should always have a trailing slash dash after the ID.

Trac ticket: https://core.trac.wordpress.org/ticket/62504

---

This Pull Request is for code review only. Please keep all other discussion in the Trac ticket. Do not merge this Pull Request. See GitHub Pull Requests for Code Review in the Core Handbook for more details.

[github-actions]

The following accounts have interacted with this PR and/or linked issues. I will continue to update these lists as activity occurs. You can also manually ask me to refresh this list by adding the props-bot label.

Core Committers: Use this line as a base for the props when committing in SVN:

Props ffffelix, azaozz, ironprogrammer.

To understand the WordPress project's expectations around crediting contributors, please review the Contributor Attribution page in the Core Handbook.

[github-actions]

Test using WordPress Playground

The changes in this pull request can previewed and tested using a WordPress Playground instance.

WordPress Playground is an experimental project that creates a full WordPress instance entirely within the browser.

Some things to be aware of

• The Plugin and Theme Directories cannot be accessed within Playground.
• All changes will be lost when closing a tab with a Playground instance.
• All changes will be lost when refreshing the page.
• A fresh instance is created each time the link below is clicked.
• Every time this pull request is updated, a new ZIP file containing all changes is created. If changes are not reflected in the Playground instance,
  it's possible that the most recent build failed, or has not completed. Check the list of workflow runs to be sure.

For more details about these limitations and more, check out the Limitations page in the WordPress Playground documentation.

Test this pull request with WordPress Playground.

[ironprogrammer]

Thanks for the patch, @ffffelix!

I was also able to reproduce this issue by unchecking and re-checking "Uncategorized" (used this Playground link that generates the terms).

To test the patch, the default Playground link works fine if you go through the repro set up steps. But try out this one that combines the repro test with the PR (takes longer to load in order to build the PR patch).

These links will look kinda nasty in Trac, but I'll share a formal test report there.