wp/5.8 branch: Restore automated testing capabilities and GitHub Actions workflows #82935

Summary

This applies the changes necessary to ensure the GitHub Actions and automated tooling in the wp/5.8 branch are in a working and maintainable state going forward.

PR stack (bottom to top)

1. Remove obsolete and trunk-only workflows (Repair wp/5.8 branch Actions: Remove obsolete and trunk-only workflows #84429)
2. Add timeouts to CI jobs that have none (Repair wp/5.8 branch Actions: Add timeouts to CI jobs that have none #84491)
3. Update GitHub Actions to their latest versions (Repair wp/5.8 branch Actions: Update GitHub Actions to their latest versions #84431)
4. Refine push branch filters (Repair wp/5.8 branch Actions: Refine push branch filters #84432)
5. Remove the mobile-unit-js job (Repair wp/5.8 branch Actions: Remove the mobile-unit-js job #84433)
6. Test against a single Node.js version (Repair wp/5.8 branch Actions: Test against a single Node.js version #84434)
7. Pin runner images instead of *-latest (Repair wp/5.8 branch Actions: Pin runner images instead of *-latest #84435)
8. Always read the Node.js version from .nvmrc (Repair wp/5.8 branch Actions: Always read the Node.js version from .nvmrc #84436)
9. Migrate wp-env to Docker Compose v2 (Repair wp/5.8 branch Actions: Migrate wp-env to Docker Compose v2 #84437)
10. Add a PHP version test matrix (Repair wp/5.8 branch Actions: Add a PHP version test matrix #84438)
11. Remove the spatie/phpunit-watcher dev dependency (Repair wp/5.8 branch Actions: Remove the spatie/phpunit-watcher dev dependency #84439)
12. Run PHP coding standards on the runner instead of inside wp-env (Repair wp/5.8 branch Actions: Run PHP coding standards on the runner instead of inside wp-env #84440)
13. Let the current Composer release install this branch's dependencies (Repair wp/5.8 branch Actions: Let the current Composer release install this branch's dependencies #84441)
14. Configure the Composer advisory policy (Repair wp/5.8 branch Actions: Configure the Composer advisory policy #84442)
15. Ignore the stale Browserslist data warning in unit tests (Repair wp/5.8 branch Actions: Ignore the stale Browserslist data warning in unit tests #84443)
16. Fix theme-activation navigation race in activate-theme.js (Repair wp/5.8 branch Actions: Fix theme-activation navigation race in activate-theme.js #84444)
17. Fetch react-native-screens as a pre-built tarball (Repair wp/5.8 branch Actions: Fetch react-native-screens as a pre-built tarball #84445)
18. Install Xdebug 3.1.6 in wp-env on PHP 7 (Repair wp/5.8 branch Actions: Install Xdebug 3.1.6 in wp-env on PHP 7 #84446)
19. Fix Test Widget e2e plugin for PHP 8 (Repair wp/5.8 branch Actions: Fix Test Widget e2e plugin for PHP 8 #84447)
20. Add a mariadbVersion option to wp-env (Repair wp/5.8 branch Actions: Add a mariadbVersion option to wp-env #84448)
21. Replace wp-env's database check with a MariaDB health check (Repair wp/5.8 branch Actions: Replace wp-env's database check with a MariaDB health check #84450)
22. Pin MariaDB to 10.6 (Repair wp/5.8 branch Actions: Pin MariaDB to 10.6 #84449)
23. Initialize WP_Block_Supports::$block_to_render and showSubmenuIcon context in the Navigation Link render tests (Repair wp/5.8 branch Actions: Initialize WP_Block_Supports::$block_to_render and showSubmenuIcon context in the Navigation Link render tests #84451)
24. Omit WordPress dependencies when scaffolding in the Create Block check (Repair wp/5.8 branch Actions: Omit WordPress dependencies when scaffolding in the Create Block check #84452)
25. Disable remote block patterns in e2e tests (Repair wp/5.8 branch Actions: Disable remote block patterns in e2e tests #84453)
26. Update the minimum supported WordPress version to 5.7 (Repair wp/5.8 branch Actions: Update the minimum supported WordPress version to 5.7 #84873)
27. Pin wp-phpunit/wp-phpunit to the WordPress 5.8 test bootstrap (Repair wp/5.8 branch Actions: Pin wp-phpunit/wp-phpunit to the WordPress 5.8 test bootstrap #84942)
28. Run PHPUnit 7.5 for PHP 7.2 and newer (Repair wp/5.8 branch Actions: Run PHPUnit 7.5 for PHP 7.2 and newer #84455)
29. Swap phpunit/phpunit for a release PHP 5.6 and 7.0 can load (Repair wp/5.8 branch Actions: Swap phpunit/phpunit for a release PHP 5.6 and 7.0 can load #84456)
30. Make the Site Editor export test compatible with PHP 5.6 and 7.0 (Repair wp/5.8 branch Actions: Make the Site Editor export test compatible with PHP 5.6 and 7.0 #84457)
31. Add wpop_keywords to the pattern directory test fixtures (Repair wp/5.8 branch Actions: Add wpop_keywords to the pattern directory test fixtures #84458)
32. Check for a current screen before reading its ID in the global styles settings (Repair wp/5.8 branch Actions: Check for a current screen before reading its ID in the global styles settings #84459)
33. Set explicit retention periods for workflow artifacts (Repair wp/5.8 branch Actions: Set explicit retention periods for workflow artifacts #84756)
34. Upload each E2E job's debug artifacts under its own name (Repair wp/5.8 branch Actions: Upload each E2E job's debug artifacts under its own name #85335)
35. Pin the PHP version used by the end-to-end tests (Repair wp/5.8 branch Actions: Pin the PHP version used by the end-to-end tests #85351)

Note: all PRs that are not marked as "ready for review" should be considered unreviewed by a human.