Fix the error that is wrong link title of a downloadable product when enabling "Use Default Value"

- Update sample title incorrectly

Author: tna274

app/code/Magento/Downloadable/Model/Sample/Builder.php

@@ -122,6 +122,12 @@ public function build(SampleInterface $sample)
         if (!$sample->getSortOrder()) {
             $sample->setSortOrder(1);
         }
+
+        $useDefaultTitle = $this->data['use_default_title'] ?? false;
+
+        if ($useDefaultTitle) {
+            $sample->setTitle(null);
+        }
         $this->resetData();
 
         return $sample;

app/code/Magento/Downloadable/Test/Unit/Model/Sample/BuilderTest.php

@@ -85,6 +85,7 @@ public function testBuild()
     {
         $data = [
             'file' => 'cXVlIHRhbA==',
+            'use_default_title' => '1',
             'type' => 'file'
         ];
         $downloadableData = ['sort_order' => 1];
@@ -123,6 +124,10 @@ public function testBuild()
             )->willReturn($fileName);
         $this->sampleMock->expects($this->once())->method('setSampleFile')->with($fileName);
         $this->sampleMock->expects($this->once())->method('setSortOrder')->with(1);
+        $useDefaultTitle = $data['use_default_title'] ?? false;
+        if ($useDefaultTitle) {
+            $this->sampleMock->expects($this->once())->method('setTitle')->with(null);
+        }
         $this->service->setData($data);
 
         $this->service->build($this->sampleMock);