fix: Don't call Job#execute() as it's deprecated

Signed-off-by: Marcel Klehr <mklehr@gmx.net>

Author: marcelklehr

tests/BackgroundJobTest.php

@@ -129,7 +129,7 @@ public function testPreviewsJob() : void {
 		// generate cached previews
 		$this->previewsJob->setId(1);
 		$this->previewsJob->setLastRun(0);
-		$this->previewsJob->execute($this->jobList);
+		$this->previewsJob->start($this->jobList);
 
 		$folder = $this->appData->getFolder('cache');
 		$newCacheSize = count($folder->getDirectoryListing());
@@ -151,7 +151,7 @@ public function testGCJob() : void {
 		// generate cached previews
 		$this->previewsJob->setId(1);
 		$this->previewsJob->setLastRun(0);
-		$this->previewsJob->execute($this->jobList);
+		$this->previewsJob->start($this->jobList);
 
 		$folder = $this->appData->getFolder('cache');
 		$cacheSize = count($folder->getDirectoryListing());