Toolset Forms 2.6 triggers fatal PHP error on earlier versions of PHP

Symptoms

Activating Toolset Forms 2.6 on earlier versions of PHP (7.1.32 or lower) produces a white screen and the following fatal PHP error:

An error of type E_COMPILE_ERROR was caused in line 10 of the file cred-frontend-editor/application/controllers/compatibility/wpml/integration/forms_translation/legacy.php. Error message: Declaration of OTGS\Toolset\CRED\Controller\Compatibility\Wpml\Integration\FormsTranslation\Legacy::register_strings($form, $form_data) must be compatible with OTGS\Toolset\CRED\Controller\Compatibility\Wpml\Integration\FormsTranslation\Base::register_strings(WP_Post $form, $form_data)

Workaround