Ensure that migration status labels can be translated

Problem/Motivation

MigrateExecutable does this
'@status' => $this->t($this->migration->getStatusLabel()),
but we need to make sure that POTX can extract the labels. The labels are defined in a class property of Migration.php.

Follow up from 📌 Fix 'Drupal.Semantics.FunctionT.NotLiteralString' coding standard Active

Steps to reproduce

Proposed resolution

TBA

Remaining tasks

Make sure the strings are available for translation.

User interface changes

API changes

Data model changes

Release notes snippet