Hook function for `hook_civirules_alter_trigger_data` is never called

I've created a custom Action in a new Civix extension here. The Action needs additional trigger data, so I've tried to hook hook_civirules_alter_trigger_data following the standard pattern of adding a myclassprefix_civirules_alter_trigger_data() function to the Civix-generated myclassprefix.php file (here).

However, my hook function is never called... verified via both XDebug and writing to the Civi debug log Civi::log()->debug(...). The custom Action itself is being called from within the rule I created.

Any suggestions how I can troubleshoot this?