Cater for variable interpolation strings in @trigger_error sniff

Problem/Motivation

The following code snippet (recently committed to 9.2 core) fails the current FunctionTriggerError sniff:

@trigger_error("StatementWrapper::\${$name} is deprecated in drupal:9.1.0 and will error in drupal:10.0.0. Access the client-level statement object via ::getClientStatement(). See https://www.drupal.org/node/3177488", E_USER_DEPRECATED);