Fix invalid icon reference in C# Android IAP demo (#1159)

mono/android_iap/project.godot

@@ -17,7 +17,7 @@ Note: Running the demo requires exporting and uploading the game to Google Play.
 config/tags=PackedStringArray("demo", "mobile", "official", "porting")
 run/main_scene="res://main.tscn"
 config/features=PackedStringArray("4.3", "C#", "Mobile")
-config/icon="res://icon.svg"
+config/icon="res://icon.webp"
 
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