Make bouncer title not selectable in talkback

The title should announce the text but should not be selectable in a11y
services.

Test: Open bouncer with talkback on.
Fixes: 260986759
Change-Id: Iaf2291754cbbfec859360721db6982ec7fcb3dff
Merged-In: Iaf2291754cbbfec859360721db6982ec7fcb3dff
(cherry picked from commit 30e756d3c7)

packages/SystemUI/res-keyguard/layout/keyguard_bouncer_message_area.xml

@@ -21,6 +21,7 @@
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
         android:layout_marginTop="@dimen/keyguard_lock_padding"
+        android:importantForAccessibility="no"
         android:ellipsize="marquee"
         android:focusable="true"
         android:gravity="center"