Reducing usage of magic constants in TAPL's widgets (fling back)

Bug: 123904290
Change-Id: I398ff2ebd418551e3fed825edf79398e32025859
diff --git a/tests/tapl/com/android/launcher3/tapl/Widgets.java b/tests/tapl/com/android/launcher3/tapl/Widgets.java
index 7d308af..6593bb1 100644
--- a/tests/tapl/com/android/launcher3/tapl/Widgets.java
+++ b/tests/tapl/com/android/launcher3/tapl/Widgets.java
@@ -64,7 +64,7 @@
                 "want to fling backwards in widgets")) {
             LauncherInstrumentation.log("Widgets.flingBackward enter");
             final UiObject2 widgetsContainer = verifyActiveContainer();
-            mLauncher.scroll(widgetsContainer, Direction.UP, 1f, MARGINS, FLING_STEPS);
+            mLauncher.scroll(widgetsContainer, Direction.UP, 1f, null, FLING_STEPS);
             try (LauncherInstrumentation.Closable c1 = mLauncher.addContextLayer("flung back")) {
                 verifyActiveContainer();
             }