Skip the review-testing-instructions workflow on PR's from community contributors

[rodelgc]

Submission Review Guidelines:

• I have followed the WooCommerce Contributing Guidelines and the WordPress Coding Standards.
• I have checked to ensure there aren't other open Pull Requests for the same update/change.
• I have reviewed my code for security best practices.
• Following the above guidelines will result in quick merges and clear and detailed feedback when appropriate.

Changes proposed in this Pull Request:

This PR adds the ability to skip the review-testing-instructions workflow when the PR is from an external contributor.
This would help unblock community PR's during the Contributor Day. See the issue reported here for context: p1681843624632139-slack-C03CPM3UXDJ

How to test the changes in this Pull Request:

Not sure if this PR could be tested, since the only way to test its changes is to have an external PR wanting to merge to trunk and the author requesting a review.

Maybe it's enough to verify that the Remind reviewers to also review the testing instructions. workflow in this PR passes.

[github-actions]

Hi @jonathansadowski, @woocommerce/solaris

Apart from reviewing the code changes, please make sure to review the testing instructions as well.

You can follow this guide to find out what good testing instructions should look like:
https://github.com/woocommerce/woocommerce/wiki/Writing-high-quality-testing-instructions

[github-actions]

Test Results Summary

Commit SHA: dfb23ea

Test 🧪	Passed ✅	Failed 🚨	Broken 🚧	Skipped ⏭️	Unknown ❔	Total 📊	Duration ⏱️
API Tests	259	0	0	2	0	261	0m 52s
E2E Tests	187	0	0	10	0	197	14m 20s

---

To view the full API test report, click here.
To view the full E2E test report, click here.
To view all test reports, visit the WooCommerce Test Reports Dashboard.

[codecov]

Codecov Report

Merging #37813 (dfb23ea) into trunk (e8fcfbb) will decrease coverage by 0.0%.
The diff coverage is n/a.

Additional details and impacted files

@@            Coverage Diff             @@
##             trunk   #37813     +/-   ##
==========================================
- Coverage     51.5%    51.5%   -0.0%     
- Complexity   17261    17280     +19     
==========================================
  Files          429      430      +1     
  Lines        79957    80026     +69     
==========================================
  Hits         41215    41215             
- Misses       38742    38811     +69     

see 3 files with indirect coverage changes

[nigeljamesstevenson]

Thanks for this Del!