Fix PHP deprecation for implicitly nullable $options in ViewsDuplicateBuilderBase

Problem/Motivation

On PHP 8.1+, a deprecation notice is triggered in Drupal\views_templates\Plugin\ViewsDuplicateBuilderBase::alterViewTemplateAfterCreation() because the $options parameter is implicitly marked as nullable. PHP now requires nullable types to be declared explicitly.

Proposed resolution

Update the method signature to explicitly declare $options as nullable (e.g. ?array or the appropriate type) to align with current PHP requirements and remove the deprecation warning.

API changes

The method signature changes to explicitly mark $options as nullable.