chore: allow forked PRs to access necessary actions secret for status checks

[jamiezieziula]

by using pull_request_target [against the main branch] it tells GHA that the workflow is trusted, and therefore can access actions secrets

relevant docs:

• https://docs.github.com/en/repositories/managing-your-repositorys-settings-and-features/enabling-features-for-your-repository/managing-github-actions-settings-for-a-repository#controlling-changes-from-forks-to-workflows-in-public-repositories
• https://securitylab.github.com/research/github-actions-preventing-pwn-requests/

[jimid27]

nice