ci: add conventional commit pr check

[alukach]

Suggesting that we add https://github.com/marketplace/actions/conventional-pull-request. It has support for both validating PR Titles and commit messages.

Also reviewed:

• https://github.com/Namchee/conventional-pr - Probably more flexible and better community support, but I got overwhelmed will all the configuration
• https://github.com/marketplace/actions/conventional-pr-title - Only focused on titles, doesn't seem to address situations where commits get their message from the only commit in single-commit PRs.