fix: PR template

[ianlewis]

Description:

Fixes the link to CONTRIBUTING.md and spacing between checklist items.

Related Issues:

N/A

Checklist:

• Review the CONTRIBUTING.md documentation.
• A reference to a related issue in the repository.
• A description of the changes proposed in the pull request.
• Please make sure to sign the Google CLA.
• Please make sure your commits include a Developer Certificate of Origin signoff.
• Please add unit tests

[codecov]

Codecov Report

Merging #523 (36c3c39) into main (6967be4) will not change coverage.
The diff coverage is n/a.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #523   +/-   ##
=======================================
  Coverage   80.32%   80.32%           
=======================================
  Files          19       19           
  Lines        1098     1098           
  Branches       14       14           
=======================================
  Hits          882      882           
  Misses        155      155           
  Partials       61       61