Fix PR Template Checkboxes

[sarahkoop]

Summary of changes

• Make PR template boxes checkable (extremely nitpick PR)

Checklist

• [ ] Added a changelog entry
• [ ] Relevant test coverage

Authors

List GitHub usernames for everyone who contributed to this pull request.

PayPal and Braintree engineering requirements

If you're an engineer for PayPal or Braintree, complete this section. For PRs from the community, please ignore!

When do these changes need to be released? [ ] ASAP (let's discuss outside this PR) [ ] Soon, here's our target release date: <DD/MM/YYYY> [ ] Whenever, no rush