[Android] Fix SigninFragmentTest.testClickingSettingsDoesNotSetFirstSetupComplete

Unable to produce this failure locally.

As discussed on the bug the reason for the failure is most probably
because SettingsActivity was not closed. Closing SettingsActivity should
resolve the failure.

The test will be enabled in a separate cl.

Bug: 1102296
Change-Id: I1cfae80f48dc84d04abb8d3e87ff7c7879987bd3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2317207
Commit-Queue: Tanmoy Mollik <triploblastic@chromium.org>
Reviewed-by: Marc Treib <treib@chromium.org>
Cr-Commit-Position: refs/heads/master@{#791451}

chrome/android/javatests/src/org/chromium/chrome/browser/signin/SigninFragmentTest.java

@@ -169,6 +169,8 @@ public class SigninFragmentTest {
         Assert.assertTrue(SyncTestUtil.isSyncRequested());
         TestThreadUtils.runOnUiThreadBlocking(
                 () -> { Assert.assertFalse(ProfileSyncService.get().isFirstSetupComplete()); });
+        // Close the SettingsActivity.
+        onView(withId(R.id.cancel_button)).perform(click());
     }
 
     @Test