Disable flaky WelcomeScreenChromeVoxHintTest.TrapFocus

The test is flaky:
https://ci.chromium.org/p/chromium/builders/ci/linux-chromeos-rel?limit=200
https://ci.chromium.org/p/chrome/builders/ci/linux-chromeos-chrome?limit=200
Sample run:
https://ci.chromium.org/ui/p/chrome/builders/ci/linux-chromeos-chrome/10767/overview

TBR=akihiroota@chromium.org
TBR=antrim@chromium.org

Bug: 1161398
Change-Id: I715d2a8426550181d73cfdec438ffe3d861f66c7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2598911Reviewed-by: Sergey Poromov <poromov@chromium.org>
Commit-Queue: Sergey Poromov <poromov@chromium.org>
Cr-Commit-Position: refs/heads/master@{#839440}

chrome/browser/chromeos/login/screens/welcome_screen_browsertest.cc

@@ -718,7 +718,8 @@ IN_PROC_BROWSER_TEST_F(WelcomeScreenChromeVoxHintTest, DismissAfterHint) {
 
 // Assert that the ChromeVox hint dialog behaves as a modal dialog and traps
 // focus when using tab.
-IN_PROC_BROWSER_TEST_F(WelcomeScreenChromeVoxHintTest, TrapFocus) {
+// TODO(crbug/1161398): The test is flaky.
+IN_PROC_BROWSER_TEST_F(WelcomeScreenChromeVoxHintTest, DISABLED_TrapFocus) {
   WelcomeScreen* screen = welcome_screen();
   OobeScreenWaiter(WelcomeView::kScreenId).Wait();
   TtsExtensionEngine::GetInstance()->DisableBuiltInTTSEngineForTesting();