Enhance PR template with due diligence checks

Added checks for AI-generated changes and testing confirmation.

Author: TobiGr

.github/PULL_REQUEST_TEMPLATE.md

@@ -32,3 +32,5 @@ The APK can be found by going to the "Checks" tab below the title. On the left p
 
 #### Due diligence
 - [ ] I read the [contribution guidelines](https://github.com/TeamNewPipe/NewPipe/blob/HEAD/.github/CONTRIBUTING.md).
+- [ ] The propsed changes are **not AI generated**.
+- [ ] I tested the changes using an emulator or a physical device.