Update call_activity.xml (#7)

add keepScreenOn true during call

 <androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
     xmlns:app="http://schemas.android.com/apk/res-auto"
     android:layout_width="match_parent"
-    android:layout_height="match_parent">
+    android:layout_height="match_parent"
+    android:keepScreenOn="true">
 
     <com.google.android.material.tabs.TabLayout
         android:id="@+id/tabs"