wp/6.4 branch: Restore automated testing capabilities and GitHub Actions workflows #82929

Summary

This applies the changes necessary to ensure the GitHub Actions and automated tooling in the wp/6.4 branch are in a working and maintainable state going forward.

PR stack (bottom to top)

1. Remove obsolete and trunk-only workflows (Repair wp/6.4 branch Actions: Remove obsolete and trunk-only workflows #83667)
2. Add timeouts to CI jobs that have none (Repair wp/6.4 branch Actions: Add timeouts to CI jobs that have none #84479)
3. Disable npm caching in release workflows (Repair wp/6.4 branch Actions: Disable npm caching in release workflows #83668)
4. Update GitHub Actions to their latest versions (Repair wp/6.4 branch Actions: Update GitHub Actions to their latest versions #83669)
5. Remove svn --version debug check (Repair wp/6.4 branch Actions: Remove svn --version debug check #83670)
6. Refine push branch filters (Repair wp/6.4 branch Actions: Refine push branch filters #83671)
7. Remove the broken flaky-test issue reporting job (Repair wp/6.4 branch Actions: Remove the broken flaky-test issue reporting job #83673)
8. Remove the mobile-unit-js job (Repair wp/6.4 branch Actions: Remove the mobile-unit-js job #83674)
9. Test against a single Node.js version (Repair wp/6.4 branch Actions: Test against a single Node.js version #83676)
10. Pin runner images instead of *-latest (Repair wp/6.4 branch Actions: Pin runner images instead of *-latest #83677)
11. Upgrade Node.js from 16 to 20 (Repair wp/6.4 branch Actions: Upgrade Node.js from 16 to 20 #83678)
12. Migrate wp-env to Docker Compose v2 (Repair wp/6.4 branch Actions: Migrate wp-env to Docker Compose v2 #83679)
13. Fix wp-env Docker builds broken by archived Debian Buster/Bullseye repositories and expired Debian Stretch signing keys (Repair wp/6.4 branch Actions: Fix wp-env Docker builds broken by archived Debian Buster/Bullseye repositories and expired Debian Stretch signing keys #83680)
14. Pin wp-env to the correct WordPress Core version (Repair wp/6.4 branch Actions: Pin wp-env to the correct WordPress Core version #83681)
15. Update the PHP version test matrix (Repair wp/6.4 branch Actions: Update the PHP version test matrix #83682)
16. Fix the Composer PHP platform override breaking unit tests on older PHP (Repair wp/6.4 branch Actions: Fix the Composer PHP platform override breaking unit tests on older PHP #83683)
17. Ignore the stale Browserslist data warning in unit tests (Repair wp/6.4 branch Actions: Ignore the stale Browserslist data warning in unit tests #83684)
18. Upgrade Playwright to fix Ubuntu 24.04 (Noble) browser-install failures (Repair wp/6.4 branch Actions: Upgrade Playwright to fix Ubuntu 24.04 (Noble) browser-install failures #83685)
19. Fix theme-activation navigation race in activate-theme.js (Repair wp/6.4 branch Actions: Fix theme-activation navigation race in activate-theme.js #83686)
20. Fix flaky Openverse image drag-and-drop e2e test (Repair wp/6.4 branch Actions: Fix flaky Openverse image drag-and-drop e2e test #83687)
21. Regenerate stale core/image deprecation fixtures (Repair wp/6.4 branch Actions: Regenerate stale core/image deprecation fixtures #83688)
22. Fix wp-bind PHP test for esc_url() scheme completion (Repair wp/6.4 branch Actions: Fix wp-bind PHP test for esc_url() scheme completion #83689)
23. Retry Puppeteer plugin activation/deactivation on timeout (Repair wp/6.4 branch Actions: Retry Puppeteer plugin activation/deactivation on timeout #83690)
24. Fix flaky interactivity router navigate e2e test (Repair wp/6.4 branch Actions: Fix flaky interactivity router navigate e2e test #83692)
25. Fix flaky site editor URL navigation e2e test (Repair wp/6.4 branch Actions: Fix flaky site editor URL navigation e2e test #83729)
26. Pass debug step arguments through to wp-env (Repair wp/6.4 branch Actions: Pass debug step arguments through to wp-env #83805)
27. Detect the database client in the debug step (Repair wp/6.4 branch Actions: Detect the database client in the debug step #83838)
28. Add a mariadbVersion option to wp-env (Repair wp/6.4 branch Actions: Add a mariadbVersion option to wp-env #83817)
29. Replace wp-env's database check with a MariaDB health check (Repair wp/6.4 branch Actions: Replace wp-env's database check with a MariaDB health check #83867)
30. Pin MariaDB to 10.11 (Repair wp/6.4 branch Actions: Pin MariaDB to 10.11 #83826)
31. Skip the flaky multiple completers autocomplete e2e test (Repair wp/6.4 branch Actions: Skip the flaky multiple completers autocomplete e2e test #84589)
32. Fix flaky Pages e2e test Save click (Repair wp/6.4 branch Actions: Fix flaky Pages e2e test Save click #84621)
33. Set explicit retention periods for workflow artifacts (Repair wp/6.4 branch Actions: Set explicit retention periods for workflow artifacts #84750)
34. Remove the unused flaky test report uploads and reporter (Repair wp/6.4 branch Actions: Remove the unused flaky test report uploads and reporter #85108)
35. Run macOS and Windows jobs only on WordPress/gutenberg (Repair wp/6.4 branch Actions: Run macOS and Windows jobs only on WordPress/gutenberg #85134)
36. Upload each E2E job's debug artifacts under its own name (Repair wp/6.4 branch Actions: Upload each E2E job's debug artifacts under its own name #85329)
37. Pin the PHP version used by the end-to-end tests (Repair wp/6.4 branch Actions: Pin the PHP version used by the end-to-end tests #85339)

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