Bug 1650607 - Change WPT test for File constructor replacement. r=baku

Change the test to follow the proposed change in w3c/FileAPI#41,
now that all browsers agree to not replace /.

Depends on D86981

Differential Revision: https://phabricator.services.mozilla.com/D87112

testing/web-platform/tests/FileAPI/file/File-constructor.html

@@ -84,7 +84,8 @@
 }
 
 test_second_argument("dummy", "dummy", "Using fileName");
-test_second_argument("dummy/foo", "dummy:foo", "Using special character in fileName");
+test_second_argument("dummy/foo", "dummy/foo",
+                     "No replacement when using special character in fileName");
 test_second_argument(null, "null", "Using null fileName");
 test_second_argument(1, "1", "Using number fileName");
 test_second_argument('', '', "Using empty string fileName");