Update FilterValidator.php

[aldok10]

fixing: trim(): Passing null to parameter 1 ($string) of type string is deprecated on PHP 8.2

Q	A
Is bugfix?	✔️
New feature?	❌
Breaks BC?	❌
Fixed issues

[what-the-diff]

PR Summary

• Implementation of New Filter Condition
  The update includes an added condition to verify if a filter is set as 'trim'. This feature will ensure that the attribute value is first turned into text format before the filter is applied. This adjustment enhances the flexibility of the filtering function, and ensures the 'trim' filter handles data correctly even when it is not in string format.

[bizley]

There is a TrimValidator for that case now, please use it.