message: fix: Update PR template to use yarn instead of npm
diff: #### Pull request checklist
  - [ ] Addresses an existing issue: Fixes #0000
  -- [ ] Added relevant unit test for your changes. (`npm run test`)
  +- [ ] Added relevant unit test for your changes. (`yarn test`)
  - [ ] Verified code coverage for the changes made. Check coverage report at: `<rootDir>/test-results/unit/coverage`
  -- [ ] Ran precheckin (`npm run precheckin`)
  +- [ ] Ran precheckin (`yarn precheckin`)
  - [ ] (UI changes only) Added screenshots/GIFs to description above
  - [ ] (UI changes only) Verified usability with NVDA/JAWS
  