Fixes failing CTS tests for Save dialog

Screenshots showing no changes from before: http://shortn/_n52tNerWx6

Test: atest CtsAutofillServiceTestCases
Bug: b/301709010
Change-Id: I29f9bcf58462d4a570f395594ab83d94fcbaff55

core/res/res/layout/autofill_save.xml

@@ -60,10 +60,11 @@
                     android:gravity="center"
                     android:textAppearance="@style/AutofillSaveUiTitle">
                 </TextView>
-                <LinearLayout
+                <FrameLayout
                     android:id="@+id/autofill_save_custom_subtitle"
                     android:layout_width="match_parent"
                     android:layout_height="wrap_content"
+                    android:minHeight="0dp"
                     android:visibility="gone"/>
 
             </LinearLayout>