chromeos: disables flaky interactive ui test

Specifically PasswordManagerInteractiveTest.PromptForXHRWithoutOnSubmit.

BUG=905789
TEST=test only change
TBR=mukai@chromium.org

Change-Id: Ia34a1d2b648964943efd137ab82a7c1082ae940a
Reviewed-on: https://chromium-review.googlesource.com/c/1338203Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Jun Mukai <mukai@chromium.org>
Commit-Queue: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#608513}

testing/buildbot/filters/chromeos.single_process_mash.interactive_ui_tests.filter

@@ -42,3 +42,6 @@
 
 # This test is flaky. https://crbug.com/897879
 -ExtensionApiTest.DisplayModeWindowIsInFullscreen
+
+# This test is flaky. https://crbug.com/905789
+-PasswordManagerInteractiveTest.PromptForXHRWithoutOnSubmit