chore: align deps, workflows, and configs with shared standards

[gin0115]

This pull request updates the project’s development and testing infrastructure to support the latest WordPress and PHP versions, improves CI configuration, and modernizes dependencies and code quality tooling. It removes support for legacy PHP versions, updates test workflows for WordPress 6.6–6.9, and introduces new code quality checks. The changes also include a custom error handler for a known WordPress 6.8 notice and update the README badges to reflect the new supported versions.

Testing and CI/CD Modernization:

• Removed the legacy .github/workflows/WP_6_4.yaml workflow, dropping support for WordPress 6.4 and PHP 7.4–8.3 in CI.
• Updated and renamed workflows for WordPress 6.6, 6.7, 6.8, and 6.9 to test against PHP 8.0–8.4 only, switched MySQL service to version 8.4, and improved Codecov integration. [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12]

Dependency and PHP Version Updates:

• Increased the minimum PHP requirement to 8.0.0, updated development dependencies to the latest compatible versions, and aligned test dependencies with the latest WordPress releases.

Code Quality and Tooling:

• Added a .scrutinizer.yml configuration to enable and customize code analysis, duplication detection, and code style checks via Scrutinizer.

Documentation and Badge Updates:

• Updated README badges to reflect the current workflows and supported PHP/WordPress versions, and added a changelog entry for version 2.1.1. [1] [2]

Testing Improvements:

• Added a custom error handler in tests/wp-config.php to suppress a known WordPress 6.8 notice about wp_is_block_theme being called too early, ensuring cleaner test output.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.29%. Comparing base (1ffb7ea) to head (9521a37).
⚠️ Report is 10 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master      #57      +/-   ##
============================================
+ Coverage     99.22%   99.29%   +0.06%     
+ Complexity      106       96      -10     
============================================
  Files            12       12              
  Lines           259      282      +23     
============================================
+ Hits            257      280      +23     
  Misses            2        2              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.