[Autofill Assistant] Disable animations for test.

I have been able to reproduce the linked issue flakily. Disabling
animations seems to fix it. The previous workaround might no longer be
necessary, but will stay in for a bit until we're sure that the issue
is indeed resolved.

Bug: 1146084
Change-Id: I6d199f19f0dbcb9ef4b10f3492566f34f96104e1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2521818
Commit-Queue: Clemens Arbesser <arbesser@google.com>
Commit-Queue: Luca Hunkeler <hluca@google.com>
Auto-Submit: Clemens Arbesser <arbesser@google.com>
Reviewed-by: Luca Hunkeler <hluca@google.com>
Cr-Commit-Position: refs/heads/master@{#824871}

chrome/android/features/autofill_assistant/javatests/src/org/chromium/chrome/browser/autofill_assistant/AutofillAssistantTriggerScriptTest.java

@@ -101,6 +101,7 @@ public class AutofillAssistantTriggerScriptTest {
 
         TestThreadUtils.runOnUiThreadBlocking(() -> {
             AssistantHeaderModel headerModel = triggerScript.getHeaderModelForTest();
+            headerModel.set(AssistantHeaderModel.DISABLE_ANIMATIONS_FOR_TESTING, true);
             headerModel.set(AssistantHeaderModel.STATUS_MESSAGE, "Hello world!");
             headerModel.set(AssistantHeaderModel.USE_STEP_PROGRESS_BAR, true);
             headerModel.set(AssistantHeaderModel.STEP_PROGRESS_BAR_ICONS,