Fix some PHP 8.1 issues in Diviner generator

Summary:
After this change I was able to generate again the Diviner
documentation from PHP 8.2 using the related command:

./bin/diviner generate

Closes T15255

Test Plan:

• run ./bin/diviner generate - great success
• tested the advanced search in various ways - it still works

Reviewers: O1 Blessed Committers, Matthew

Reviewed By: O1 Blessed Committers, Matthew

Subscribers: Ekubischta, speck, tobiaswiese, Matthew, Cigaryno

Maniphest Tasks: T15226, T15255

Differential Revision: https://we.phorge.it/D25124