AI: Update PHP AI Client package to 1.3.1.

This package update fixes two bugs related to parsing function calls and function responses.

See release: https://github.com/WordPress/php-ai-client/releases/tag/1.3.1

See #64591.


git-svn-id: https://develop.svn.wordpress.org/trunk@62046 602fd350-edb4-49c9-b593-d223f7449a82