fix deprecated assert

package_manager/tests/src/Kernel/PathExcluder/UnknownPathExcluderTest.php

@@ -200,7 +200,7 @@ class UnknownPathExcluderTest extends PackageManagerKernelTestBase {
     $config->set('include_unknown_files_in_project_root', FALSE)->save();
     $this->assertFileExists($project_root . '/unknown/file.txt');
     $stage->create();
-    $this->assertFileNotExists($stage->getStageDirectory() . '/unknown/file.txt');
+    $this->assertFileDoesNotExist($stage->getStageDirectory() . '/unknown/file.txt');
   }
 
 }