Add flag override for MultiDeviceSlipperyWindowTest

This test currently assumes that the flag is enabled, and fails on
platforms where that's not the case.

Bug: 337200792
Test: atest --host inputflinger_tests
Change-Id: Ia789128f40ec2ea809b46a47ca7947a0fbe5ac3a
diff --git a/services/inputflinger/tests/InputDispatcher_test.cpp b/services/inputflinger/tests/InputDispatcher_test.cpp
index 8ad235f..8de28c6 100644
--- a/services/inputflinger/tests/InputDispatcher_test.cpp
+++ b/services/inputflinger/tests/InputDispatcher_test.cpp
@@ -7814,6 +7814,7 @@
  * If device B reports more ACTION_MOVE events, the middle window should receive remaining events.
  */
 TEST_F(InputDispatcherTest, MultiDeviceSlipperyWindowTest) {
+    SCOPED_FLAG_OVERRIDE(enable_multi_device_same_window_stream, true);
     std::shared_ptr<FakeApplicationHandle> application = std::make_shared<FakeApplicationHandle>();
     sp<FakeWindowHandle> leftWindow =
             sp<FakeWindowHandle>::make(application, mDispatcher, "Left window",