Upgrade to oik-css v2.4.0 for accessibility improvements for Low Color Contrast errors.

Changes
| Change | Reference |
|---|---|
| Changed: Support PHPUnit 10 & 11. | bobbingwide/oik-css#27 |
| Changed: Accessibility: Update test data results | bobbingwide/oik-css#19 |
| Changed: Accessibility: Deal with more GeSHi low color contrast messages from WAVE | bobbingwide/oik-css#19 |
| Changed: Fixed: Accessibility – don’t run wpautop() on the_excerpt | bobbingwide/oik-css#19 |
| Changed: Accessibility: Deal with more GeSHi low color contrast messages from WAVE | bobbingwide/oik-css#19 |
| Changed: Accessibility: Use grid rather than table | bobbingwide/oik-css#19 |
| Fixed: Support PHP 8.4 | bobbingwide/oik-css#27 |
| Changed: Fix Color Contrast errors from WAVE for GeSHi’d output | bobbingwide/oik-css#19 |
Tested
- Tested: With WordPress 6.9 and WordPress Multisite
- Tested: With PHP 8.4
- Tested: With PHPUnit 10 & 11
