Fixed PHPStan

Author: slavvka

app/code/Magento/Catalog/Test/Unit/Model/Product/TierPriceManagementTest.php

@@ -142,6 +142,7 @@ public function testGetList($configValue, $customerGroupId, $groupData, $expecte
             ->method('getValue')
             ->with('catalog/price/scope', ScopeInterface::SCOPE_WEBSITE)
             ->willReturn($configValue);
+        $priceMock = null;
         if ($expected) {
             $priceMock = $this->getMockForAbstractClass(ProductTierPriceInterface::class);
             $priceMock->expects($this->once())