www/kanboard: update to 1.2.31

ChangeLog: https://github.com/kanboard/kanboard/releases/tag/v1.2.31

Security Fixes:

• CVE-2023-36813: Avoid potential SQL injections without breaking compatibility with plugins

Other fixes and updates:

• Run tests with PHP 8 on GitHub Actions
• Bump Symfony dependencies
• Update Composer dependencies to be able to run tests with PHP 8.2
• Add /usr/bin/php symlink in the Docker image
• Replace usage of at() matcher with alternatives in unit tests
• Adjust plugin directory test case to work on released versions
• Fix incorrect background dynamic property in captcha library
• Update translations

Reported by: portscout
MFH: 2023Q3 (security fix)
Security: CVE-2023-36813

(cherry picked from commit a4f1bfb9fb0fc1d03298cddf28433823d3d5764c)