Fix visual bug with release note mute with a background.

app/src/main/res/layout/conversation_activity_unmute.xml

@@ -1,7 +1,8 @@
 <?xml version="1.0" encoding="utf-8"?>
 <FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
     android:layout_width="match_parent"
-    android:layout_height="wrap_content">
+    android:layout_height="wrap_content"
+    android:background="@color/signal_background_primary">
 
     <com.google.android.material.button.MaterialButton
         android:id="@+id/conversation_activity_unmute_button"