.github: Update pull_request_template.md

[leiflindholm]

Description

Slightly reword the template to be more specific and use active language.

• [ ] Breaking change?
  • Breaking change - Will this cause a break in build or boot behavior?
  • Examples: Add a new library class or move a module to a different repo.
• [ ] Impacts security?
  • Security - Does the change have a direct security impact?
  • Examples: Crypto algorithm change or buffer overflow fix.
• [ ] Includes tests?
  • Tests - Does the change include any explicit test code?
  • Examples: Unit tests or integration tests.

How This Was Tested

<Describe the test(s) that were run to verify the changes.>

Integration Instructions

<Describe how these changes should be integrated. Use N/A if nothing is required.>