Drupal 9 broken by missing requirements getter

Documenting this here in case there's a way to work around it but currently migrate_manifest is unable to upgrade to Drupal 9 because a required method on Migration was removed without a replacement.

$required_ids = $migration->get('requirements'); which is used for expanding and merging required migrations.

Error: Call to undefined method Drupal\migrate\Plugin\Migration::get() in /app/modules/migrate_manifest/src/MigrateManifest.php on line 155 #0 /app/modules/migrate_manifest/src/MigrateManifest.php(106): Drupal\migrate_manifest\MigrateManifest->injectDependencies(Object(Drupal\migrate\Plugin\Migration), Array)
#1 /app/modules/migrate_manifest/src/Commands/MigrateManifestCommands.php(50): Drupal\migrate_manifest\MigrateManifest->import('initial-01-user...')
#2 [internal function]: Drupal\migrate_manifest\Commands\MigrateManifestCommands->manifest('initial-01-user...', Array)
#3 /app/vendor/consolidation/annotated-command/src/CommandProcessor.php(257): call_user_func_array(Array, Array)
#4 /app/vendor/consolidation/annotated-command/src/CommandProcessor.php(212): Consolidation\AnnotatedCommand\CommandProcessor->runCommandCallback(Array, Object(Consolidation\AnnotatedCommand\CommandData))
#5 /app/vendor/consolidation/annotated-command/src/CommandProcessor.php(176): Consolidation\AnnotatedCommand\CommandProcessor->validateRunAndAlter(Array, Array, Object(Consolidation\AnnotatedCommand\CommandData))
#6 /app/vendor/consolidation/annotated-command/src/AnnotatedCommand.php(302): Consolidation\AnnotatedCommand\CommandProcessor->process(Object(Symfony\Component\Console\Output\ConsoleOutput), Array, Array, Object(Consolidation\AnnotatedCommand\CommandData))
#7 /app/vendor/symfony/console/Command/Command.php(255): Consolidation\AnnotatedCommand\AnnotatedCommand->execute(Object(Drush\Symfony\DrushArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#8 /app/vendor/symfony/console/Application.php(1018): Symfony\Component\Console\Command\Command->run(Object(Drush\Symfony\DrushArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#9 /app/vendor/symfony/console/Application.php(271): Symfony\Component\Console\Application->doRunCommand(Object(Consolidation\AnnotatedCommand\AnnotatedCommand), Object(Drush\Symfony\DrushArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#10 /app/vendor/symfony/console/Application.php(147): Symfony\Component\Console\Application->doRun(Object(Drush\Symfony\DrushArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#11 /app/vendor/drush/drush/src/Runtime/Runtime.php(118): Symfony\Component\Console\Application->run(Object(Drush\Symfony\DrushArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#12 /app/vendor/drush/drush/src/Runtime/Runtime.php(49): Drush\Runtime\Runtime->doRun(Array, Object(Symfony\Component\Console\Output\ConsoleOutput))
#13 /app/vendor/drush/drush/drush.php(72): Drush\Runtime\Runtime->run(Array)
#14 /app/vendor/drush/drush/drush(4): require('/app/vendor/dru...')
#15 {main}