fix: glance_default_loading_layout.xml round corners for API < 31

Author: jvsena42

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

@@ -2,7 +2,7 @@
 <FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
-    android:background="#FF2A2A2A"
+    android:background="@drawable/appwidget_background"
     android:padding="16dp">
 
     <TextView