Update Shipment Line Items by SKU

Updates the line items for a specific shipment, identifying each item by SKU instead of inventory id. The SKU matches both the ShipBob variant SKU and the channel seller SKU. The request body must include the complete list of line items — partial updates are not supported. Retrieve the current line items first (via GET /shipment/{shipmentId}:getLineItems, which returns each item's `product_variant.sku`), modify the desired fields, and submit the full payload. **SKU resolution:** Resolution is all-or-nothing — if any SKU in the request cannot be resolved, the whole request fails and no update occurs. A SKU that resolves to a bundle or to multiple inventory items is rejected with a per-item error; use the inventory_id-based endpoint (:updateLineItems) for those items. **Important:** The `is_manually_assigned_lot` field must be set to the same value for all line items in the request. When set to `true` on any item, ShipBob treats all lot assignments in the shipment as manually reviewed — ShipBob will not auto-assign or re-optimize lots for any item. When set to `false`, ShipBob manages lot selection automatically. Mixing `true` and `false` across items in the same request will result in a validation error. **Note on error handling:** This endpoint returns HTTP 200 for both successful and failed operations. Always check the `is_success` field in the response body to determine the outcome. When `is_success` is `false`, the `error` object contains the error code and message. HTTP 400 is only returned when the request body itself is missing or empty.