MAGETWO-75460: [Backport] - LowestPriceOptionsProvider returns products without attributes which are used for price calculation (e.g. tax adjustment)

- Update unit test;

Author: adifucan

app/code/Magento/ConfigurableProduct/Test/Unit/Pricing/Price/LowestPriceOptionsProviderTest.php

@@ -90,7 +90,7 @@ public function testGetProducts()
         $this->productCollection
             ->expects($this->once())
             ->method('addAttributeToSelect')
-            ->with(['price', 'special_price', 'special_from_date', 'special_to_date'])
+            ->with(['price', 'special_price', 'special_from_date', 'special_to_date', 'tax_class_id'])
             ->willReturnSelf();
         $this->productCollection->expects($this->once())->method('addIdFilter')->willReturnSelf();
         $this->productCollection->expects($this->once())->method('getItems')->willReturn($linkedProducts);