Update PR template sections

[jeffpaul]

Updated the pull request template within the sections for AI tool usage, testing instructions, screenshots, and changelog entries.

What?

This PR adds AI usage example, simplifies the testing + screenshot section akin to the Two-Factor repo, and adds a Changelog entry section to help with release preparation work.

Copilot summary

This pull request updates the .github/PULL_REQUEST_TEMPLATE.md file to improve clarity and completeness for contributors. The main changes include restructuring sections for AI tool disclosure, expanding instructions for testing and screenshots, and adding a new section for changelog entries.

Template improvements:

• Clarified and expanded the "Use of AI Tools" section, including an example disclosure format and explicit fields for tool, model, and usage details.
• Updated "Testing Instructions" to request clear steps for validating changes, and improved the format for listing instructions.
• Enhanced the "Screenshots or screencast" section with clearer instructions and a cleaner table format for before/after comparisons.

Changelog management:

• Added a new "Changelog Entry" section with guidance and examples for summarizing the type of change (e.g., Added, Changed, Fixed, Security).

Why?

How?

Use of AI Tools

Testing Instructions

Testing Instructions for Keyboard

Screenshots or screencast

Before	After

[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.

If you're merging code through a pull request on GitHub, copy and paste the following into the bottom of the merge commit message.

Co-authored-by: jeffpaul <jeffpaul@git.wordpress.org>
Co-authored-by: dkotter <dkotter@git.wordpress.org>

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

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 68.31%. Comparing base (274a2da) to head (6550462).
⚠️ Report is 2 commits behind head on develop.

Additional details and impacted files

@@            Coverage Diff             @@
##             develop     #429   +/-   ##
==========================================
  Coverage      68.31%   68.31%           
  Complexity       812      812           
==========================================
  Files             53       53           
  Lines           3939     3939           
==========================================
  Hits            2691     2691           
  Misses          1248     1248           

Flag	Coverage Δ
unit	68.31% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.