Add new Testing Instructions section to PR template.

[alexstine]

Description

This adds a new section called Testing Instructions to the PR template. That way contributors can better understand exactly how to test a PR by following simple steps.

How has this been tested?

GitHub template change.

Screenshots

Types of changes

Workflow modification.

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.

[noisysocks]

We already have "How has this been tested" which is supposed to cover this. I like the copy that you wrote better, though. How about we delete "How have this been tested" and keep "Testing instructions"?

[alexstine]

@noisysocks Sounds good. Updated.

[talldan]

I think this is a good improvement, so giving it the thumbs up 👍

[getdave]

I'm all for this. I still find too many PRs where the author describes that they have tested it rather than how the reviewer should test it.

Thanks for the PR!

[Mamaduka]

It is a good improvement. Let's merge it