Fix issue template typo

[jasmussen]

Description

Followup to #37780, which added a schema checkbox to the GitHub issue template. There were two small typos in the change which mean the checkbox didn't render as a checkbox, and the HTML comment wasn't hidden, see the last row in this screenshot:

This PR fixes the typo so the template should render a checkbox and hide the HTML comment.

How has this been tested?

Not actually sure how to test this.

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• I've tested my changes with keyboard and screen readers.
• My code has proper inline documentation.
• I've included developer documentation if appropriate.
• I've updated all React Native files affected by any refactorings/renamings in this PR (please manually search all *.native.js files for terms that need renaming or removal).
• [] I've updated related schemas if appropriate. <!-- Reference: https://github.com/WordPress/gutenberg/tree/trunk/schemas ->

[ryanwelcher]

LGTM 👍