Fix typo in property name

Author: akiojalehto

app/code/Magento/SalesInventory/Test/Unit/Model/Plugin/Order/Validation/InvoiceRefundCreationArgumentsTest.php

@@ -33,7 +33,7 @@ class InvoiceRefundCreationArgumentsTest extends \PHPUnit\Framework\TestCase
     /**
      * @var CreditmemoCreationArgumentsExtensionInterface|\PHPUnit_Framework_MockObject_MockObject
      */
-    private $extencionAttributesMock;
+    private $extensionAttributesMock;
 
     /**
      * @var CreditmemoCreationArgumentsInterface|\PHPUnit_Framework_MockObject_MockObject
@@ -75,7 +75,7 @@ protected function setUp()
             ->disableOriginalConstructor()
             ->getMock();
 
-        $this->extencionAttributesMock = $this->getMockBuilder(CreditmemoCreationArgumentsExtensionInterface::class)
+        $this->extensionAttributesMock = $this->getMockBuilder(CreditmemoCreationArgumentsExtensionInterface::class)
             ->setMethods(['getReturnToStockItems'])
             ->disableOriginalConstructor()
             ->getMockForAbstractClass();
@@ -111,9 +111,9 @@ public function testAfterValidation($erroMessage)
         $returnToStockItems = [1];
         $this->creditmemoCreationArgumentsMock->expects($this->exactly(3))
             ->method('getExtensionAttributes')
-            ->willReturn($this->extencionAttributesMock);
+            ->willReturn($this->extensionAttributesMock);
 
-        $this->extencionAttributesMock->expects($this->exactly(2))
+        $this->extensionAttributesMock->expects($this->exactly(2))
             ->method('getReturnToStockItems')
             ->willReturn($returnToStockItems);