Return value of Migration\ResourceModel\AbstractCollection::key() must be an instance of Migration\ResourceModel\mixed, int returned

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### Preconditions

1. Magento 1.9.3.10 to Magento 2.4.5
2. PHP 7.4 & MySQL 8.0.30 - Ubuntu 22.04.1
3. FRESH Magento 2 install

### Steps to reproduce

1. Run - composer require magento/data-migration-tool:~2.4.5
2. Create and configure a Migration module in app/code/Vendor/Migration following steps in official docs
4. Check data integrity and add ignores for tables and fields that are flagged as problematic i.e. 3rd party extensions
5. Run - php bin/magento migrate:settings --reset app/code/Vendor/Migration/etc/opensource-to-opensource/1.9.3.10/config.xml

### Expected result
[2022-09-08T11:15:47.605990+00:00][INFO][mode: settings][stage: integrity check][step: Settings Step]: started
100% [============================] Remaining Time: < 1 sec
[2022-09-08T11:15:47.632163+00:00][INFO][mode: settings][stage: integrity check][step: Stores Step]: started
100% [============================] Remaining Time: < 1 sec
[2022-09-08T11:15:47.652288+00:00][INFO][mode: settings][stage: data migration][step: Settings Step]: started
100% [============================] Remaining Time: < 1 sec
[2022-09-08T11:15:49.870886+00:00][INFO][mode: settings][stage: data migration][step: Stores Step]: started
100% [>---------------------------] Remaining Time: < 1 sec

### Actual result
[2022-09-08T11:15:47.605990+00:00][INFO][mode: settings][stage: integrity check][step: Settings Step]: started
100% [============================] Remaining Time: < 1 sec
[2022-09-08T11:15:47.632163+00:00][INFO][mode: settings][stage: integrity check][step: Stores Step]: started
100% [============================] Remaining Time: < 1 sec
[2022-09-08T11:15:47.652288+00:00][INFO][mode: settings][stage: data migration][step: Settings Step]: started
100% [============================] Remaining Time: < 1 sec
[2022-09-08T11:15:49.870886+00:00][INFO][mode: settings][stage: data migration][step: Stores Step]: started
0% [>---------------------------] Remaining Time: < 1 secReturn value of Migration\ResourceModel\AbstractCollection::key() must be an instance of Migration\ResourceModel\mixed, int returned#0 /var/www/html/magento2/vendor/magento/data-migration-tool/src/Migration/ResourceModel/AbstractCollection.php(69): Migration\ResourceModel\AbstractCollection->key()
#1 /var/www/html/magento2/vendor/magento/data-migration-tool/src/Migration/ResourceModel/Destination.php(38): Migration\ResourceModel\AbstractCollection->valid()
#2 /var/www/html/magento2/vendor/magento/data-migration-tool/src/Migration/Step/Stores/Data.php(118): Migration\ResourceModel\Destination->saveRecords()
#3 /var/www/html/magento2/vendor/magento/data-migration-tool/src/Migration/Mode/AbstractMode.php(82): Migration\Step\Stores\Data->perform()
#4 /var/www/html/magento2/vendor/magento/data-migration-tool/src/Migration/Mode/Settings.php(100): Migration\Mode\AbstractMode->runStage()
#5 /var/www/html/magento2/vendor/magento/data-migration-tool/src/Migration/Mode/Settings.php(58): Migration\Mode\Settings->runData()
#6 /var/www/html/magento2/vendor/magento/data-migration-tool/src/Migration/Console/MigrateSettingsCommand.php(59): Migration\Mode\Settings->run()
#7 /var/www/html/magento2/vendor/symfony/console/Command/Command.php(255): Migration\Console\MigrateSettingsCommand->execute()
#8 /var/www/html/magento2/vendor/magento/framework/Interception/Interceptor.php(58): Symfony\Component\Console\Command\Command->run()
#9 /var/www/html/magento2/vendor/magento/framework/Interception/Interceptor.php(138): Migration\Console\MigrateSettingsCommand\Interceptor->___callParent()
#10 /var/www/html/magento2/vendor/magento/framework/Interception/Interceptor.php(153): Migration\Console\MigrateSettingsCommand\Interceptor->Magento\Framework\Interception\{closure}()
#11 /var/www/html/magento2/generated/code/Migration/Console/MigrateSettingsCommand/Interceptor.php(77): Migration\Console\MigrateSettingsCommand\Interceptor->___callPlugins()
#12 /var/www/html/magento2/vendor/symfony/console/Application.php(1009): Migration\Console\MigrateSettingsCommand\Interceptor->run()
#13 /var/www/html/magento2/vendor/symfony/console/Application.php(273): Symfony\Component\Console\Application->doRunCommand()
#14 /var/www/html/magento2/vendor/magento/framework/Console/Cli.php(116): Symfony\Component\Console\Application->doRun()
#15 /var/www/html/magento2/vendor/symfony/console/Application.php(149): Magento\Framework\Console\Cli->doRun()
#16 /var/www/html/magento2/bin/magento(23): Symfony\Component\Console\Application->run()
#17 {main}

### Additional notes
The error: Return value of Migration\ResourceModel\AbstractCollection::key() must be an instance of Migration\ResourceModel\mixed, int returned

I have not been able to find anything related to this error. Is there a compatibility issue with 2.4.5?

Please advise.

Start by running the reported `migrate:settings --reset` command and trace the failure through `src/Migration/ResourceModel/AbstractCollection.php`, `Destination.php`, and `Step/Stores/Data.php`. Check how `key()` is used by `valid()` and confirm the migration completes without the return-type error; use the stack trace as the initial test path.

Written by the indexing model from the issue text.