Calling static trait method EntityReferenceDeltaFilterTrait::getFieldOptions is deprecated

Problem/Motivation

As of PHP 8, static trait methods can't be called. This is happening here:

EntityReferenceDeltaFilterTrait::getFieldOptions($this->fieldDefinition),

Steps to reproduce

Try to load the formatter on the Manage Display of a node. It won't work because of the error:
Got error 'PHP message: PHP Deprecated: Calling static trait method Drupal\\entityreference_extensions\\EntityReferenceDeltaFilterTrait::getFieldOptions is deprecated, it should only be called on a class using the trait in web/modules/contrib/entityreference_extensions/src/EntityReferenceDeltaFilterTrait.php on line 224'

Proposed resolution

Replace the trait name by "self" in EntityReferenceDeltaFilterTrait.php:224