Default source check missing on source item decrement for Legacy stock status update

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### Preconditions (*)

1. Magento Inventory Version: 1.2.1-p1, develop
2. Magento Version 2.4.3-p1

### Steps to reproduce (*)

1. Decrement a source item for a source that is not the Default source

### Expected result (*)

1. The legacy stock status should not be updated if the decremented source item is not for the default source

### Actual result (*)

1. Legacy stock status is updated regardless of the source code

There is missing source code check at the beginning of the for loop in the SynchronizeLegacyStockAfterDecrementStockPlugin plugin
https://github.com/magento/inventory/blob/develop/InventoryCatalog/Plugin/InventoryApi/SynchronizeLegacyStockAfterDecrementStockPlugin.php#L102

The check is already implemented in \Magento\InventoryCatalog\Model\ResourceModel\DecrementQtyForLegacyStock called a line 99
https://github.com/magento/inventory/blob/develop/InventoryCatalog/Plugin/InventoryApi/SynchronizeLegacyStockAfterDecrementStockPlugin.php#L99

Start with InventoryCatalog/Plugin/InventoryApi/SynchronizeLegacyStockAfterDecrementStockPlugin.php at the referenced loop and compare its handling with Magento\InventoryCatalog\Model\ResourceModel\DecrementQtyForLegacyStock around line 99. Verify the source-code condition for a non-default source, then run the relevant inventory tests if available; done means legacy stock status is unchanged for non-default sources.

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